Question 866279
Hypotenuse of 1st Triangle=15

Leg a of 1st Triangle=y+3


Hypotenuse of 1st Triangle=15
Leg b of 2nd Triangle=6
Leg a of 2nd Triangle=8
Hypotenuse of 2nd Triangle=10
I see that we are dealing with multiples of 3 4 5 right triangles
                b  a  H
second triangle 6  8 10
first triangle  9 12 15
y+3=12
y=9

The way that you chose
15/10=(y+3)/8 
3/2=(y+3)/8
24=2*(y+3)
12=y+3
9=y