What’s the missing side length??

y = 24

Step-by-step explanation:

Use Pythagerean Theorem:

a^2 + b^2 = c^2

10^2 + b^2 = 26^2

100 + b^2 = 676

b^2 = 576

b = 24

b = y

the answer is (4,3)

since the rule for r0, 90º is (-y,x) and it was already applied to form the image, all you have to do is reverse the answer using this formula.