the cost c of a car service is partly constant and partly varies with time t it takes to the work .if it costs #5 and half hours service and #29 for a 4 hours services.(a)find the formula connecting the cost c and time t (b)find the cost of a 7 and half hours service
c = at+b
now, just solve
0.5a + b = 5
4a + b = 29
to find a and b,
and then find c(7.5)