Sorry I'm getting really confused here!

Here is the full detail of how I've attempted to solve it:

g=50

h=100

i=70

j=15

Which gives:

1) d = a - (b /2)

2) e = d + b

3) f = p - (c /2)

4) 50 = f - (d /2)

5) 100 = 50 + d

6) 70 = f - (e /2) + c

7) 15 = 70 + e

First I solve e by using 7):

15 = 70 + e

70 + e = 15

(-70 both sides)

e = -55

Which means that e = j-i

Now solve d using equation 5):

100 = 50 + d

50 + d = 100

(-50 from both sides)

d = 50

Which means that d = h-g

Now I solve f using equation 4):

50 = f - (d /2)

f - (d /2) = 50

Sub d since we know it

f - (50 /2) = 50

f - 25 = 50

(add 25 to both sides)

f = 75

which means that f = g + (d/2)

Now solve c using equation 6):

70 = f - (e /2) + c

f - (e /2) + c = 70

Sub f as we know its value

75 - (e /2) + c = 70

Sub e as we know its value

75 - (-55 /2) + c = 70

102.5 + c = 70

(-102.5 from both sides)

c = -32.5

Which means c = f -( e/2)

Now solve P using equation 3):

f = p - (c /2)

Sub f

75 = p - (c /2)

Sub c

75 = p - (-32.5 /2)

75 = p - (-16.25)

(Add 16.25 to both sides)

91.25 = p or

p = 91.25

You haven't considered the order of operations. Multiplication should be done before addition. So -16.25 should be multiplied by -1 before adding whatever necessary to subject p.

75 = p - (-16.25)

75=p+16.25

75-16.25=p

p=58.75
Which means p = f + (c/2)

Now solve b using equation 2):

e = d + b

Sub e

-55 = d + b

Sub d

-55 = 50 + b

(-50 from both sides)

-105 = b or

b = -105

Which means b = e-d

Finally solve a using equation 1):

d = a - (b /2)

Sub d

50 = a - (b /2)

Sub b

50 = a - (-105 /2)

50 = a - (-52.5)

(+52.5 to both sides)

102.5 = a or

a = 102.5 Again the same mistake as earlier. I hope you can correct it now.
Which means a = d + (b/2)

So:

a=102.5 (wrong somehow..)

b=-105

c=-32.5

d=50

e=-55

f=75

p=91.25 (wrong somehow..)

Testing gives:

1) 50 = 102.5 - (-105 /2) (wrong because 155)

2) -55 = 50 + -105 (ok)

3) 75 = 91.25 - (-32.5 /2) (wrong because 107.5)

4) 50 = 75 - (50 /2) (ok)

5) 100 = 50 + 50 (ok)

6) 70 = 75 - (-55 /2) + -32.5 (ok)

7) 15 = 70 + -55 (ok)

So I can see I've still managed to get the values of a and p wrong?