A friend says - 3/5y - 1/7y = 910 is y = 676. What mistake was made?

1st step: get a common denominator

-3/5y - 1/7y = 910

-3/5 = - 15/35

-1/7 = - 5/35

2nd step: subtract and reduce

-15/35y - 5/35y = 910

-20/35y = 910

-4/7y = 910

3rd step: multiply both sides by the reciprocal

(-7/4) (-4/7y) = 910 (-7/4)

y = - 1592.5

the mistake was that they did not have common denominators in order to subtract correctly and so it shifted the whole process