Use the Pythagoras theorum: a^2 + b^2 = c^2
Question 1:
15^2 = x^2 + 12^2
225 = x^2 + 144
x^2 = 225 - 144
x^2 = 81
Square root both sides to get x;
x = 9cm
Question 2:
3^2 + 4^2 = y^2
9 + 16 = y^2
y^2 = 25
Square root both sides to get y;
y = 5cm
Hope this helps!
(I haven't done question 3 and 4 because I can't see them in the image. Please type them in the comments so I can help you with them.)
