Answer:
r =5
Step-by-step explanation:
We can use the Pythagorean theorem
a^2 + b^2 = c^2
The legs are r and 12
The hypotenuse is (8+r)
r^2 + 12^2 = (8+r)^2
r^2 + 144 = 64 + r^2 +16r
Subtract r^2 from each side
144 = 64 +16r
Subtract 64 from each side
144-64 = 16r
80 = 16r
Divide each side by 16
80/16 = 16r/16
5 =r
