this problem confused me.

-5/-7x + -1/5x = - 3/5

-5/-7x+-1/5x=-3/5

5/7x-1/5x=-3/5
25/35x-7/35x=-21/35
18/35x=-21/35
Multiply each side by 35/18.
x=-7/6 or -1 1/6