Write and solve an equation, as follows:
-7y + 5(3+ny) = 3y + 15. We are to find the value of 'n.'
-7y + 15 + 5ny = 3y + 15.
Subtracting 15 from both sides, we get -7y + 5ny = 3y
Grouping like terms, we get 5ny = 3y + 7y = 10y
Dividing both sides by 5y, we get n = 2 (answer)