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