Surd Problem Help needed

Points A and B have coordinates (-1,2) and (4,7) respectively
(a) write down the coordinates of M, the midpoint of AB
(b) calculate the distance AB
(c) The point p lies on the circle with AB as diameter and has coordinates (2, Y) where y is positive. Calculate the value of y giving your answer in surd form


My Ans:
(a)
Mid point: ( -1+7)/2, (2-4) /2 = (3,-1)
Distance MB=

sqrt((7-3)^2+(-4+1)^2= 16+9= 25 = sqrt(25)= 5 But the answer is 10
(c) I am not sure I tried (x-h)^2+ (y-k)^2= r^2 but notgetting

It usually helps if, where you can, you draw a diagram. It need only be a sketch.
Do this here, and you should see that your calculation for the mid-point is incorrect.
Add to your diagram two lines parallel with the co-ordinate axes so as to form a right angled triangle and then use the Pythagoras theorem to calculate the length of the hypotenuse (the distance between A and B), and BTW, the answer that you give, 10, is not correct.
The equation that you give for the circle is correct, you have to fill in the co-ordinates of its centre, the mid-point of AB, and its radius, half the length of AB.