Answer:
y = 8
Explanation:
A 3-4-5 right triangle, and its multiples, are the only ones with rational side lengths in the ratio 3:5. In other words, the 6y : 10y side ratios mean that ...
3 : 4 : 5 = 6y : 64 : 10y
or
64 = 8y
y = 8 . . . . . . . divide by 8