Your first question is strange. I suppose its not looking for a concrete answer. in the first case, just isolate s to one side.

A-115-1/2p=1/2s

2A-230-p=s

Try this for the second one.

The perimeter of standard - size copier papper is 99 cm. The width is 6.3 cm less than the length. Find the length and the width.

Let x be length and y be width.

Perimeter = x+y+x+y = 2x+2y

99=2x+2y

y=x-6.3

Substituting, we get...

99=2x+2(x-6.3)

99=4x-12.6

111.6=4x

x=27.9cm

We know y is 6.3 less than this so,

y=21.6cm