math linear please help

Question

Bob makes outdoor tables. He charges a fixed price for the materials required to build the table and also an hourly rate for the time spent constructing. The amount he charges $C, is given by C = 60n + 120, where n is the number of labour hours. 

Answer 1

C=60n+120

he charges $60 per hour

fixed price for materials = $120

for a table that requires 4.5 hours the cost = C=60(4.5)+120= 270+120 = $390

for a table that costs $540, the hours required are n in the equation 540=120+60n

60n = 540-120 = 420

n = 420/60= 7 hours