a.
'the product of a number y and 3' = Y * 3
'five more than the product....' = 5 + (Y * 3)
The expression that can be used to model this phrase is 5 + 3Y.
b.
'the quotient of a number N and 4' = N ÷ 4
'seven less than the quotient...' = (N ÷ 4) - 7
The expression that can be used to model this phrase is (N ÷ 4) - 7.