Which expression is equivalent to 4.2 + x+2y+y+y+ help me ASAP

Ateacher has $80 to buy workbooks. each work book cost $3. if she buys as many workbooks as possible, how much money does she have leftover? a) $2 b) $4 c) $6 d) $8

An advertising firm has an old computer that can prepare a whole mailing in 6 hours. with the of newer model the job is complete in 2 hours. how long would it take the newer model to do the job alone?

If 10 men take 18 days to mow 60 acres of grass, how long will 15 men take to mow 80 acres?