Answer:
C(h) = 50h + 25 
$425
Explanation:
Et the plumber works for h hours. 
Cost of one hour = $50
Therefore, cost of h hours = $50h
Total cost = cost of h hours + plumber service call charge
C(h) = 50h + 25 (required equation) 
Plug h = 8
C(8) = 50* 8 + 25 = 400 + 25 = $425