Hey there!
C = 0.25x + 40
(a) For this part we solve for C when x = 240. Substitute 240 in for x.
C = 0.25(240) + 40
Multiply 240 by 0.25.
C = 60 + 40
Add.
C = 100
The cost is $100.
Check
100 = 0.25(240) + 40
100 = 60 + 40
100 = 100
(b) For this part we solve for x when C = 180. Substitute 180 for C.
180 = 0.25x + 40
Subtract 40 from each side.
140 = 0.25x
Divide each side by 0.25.
560 = x
This person drove 560 miles.
Check
180 = 0.25(560) + 40
180 = 140 + 40
180 = 180
(c) For this we must make an inequality with C = 150.
Since they want the cost to be no more than 150, we will use the ≥ symbol.
C ≥ 0.25x + 40
Substitute 150 for C. Solve for x.
150 ≥ 0.25x + 40
Subtract 40 from each side.
110 ≥ 0.25x
Divide each side by 0.25.
440 ≥ x
The max number of miles they can drive is 440.
Check
150 ≥ 0.25(440) + 40
150 ≥ 110 + 40
150 ≥ 150
Hope this helps!