A NEW OG 2021 QUESTION
The question here tests on skills in Unitary Methods.
"c" is the FIXED Charge to be paid and hence PRESENT IN ALL OPTIONS.
Beyond "50" hrs, the x-50 hrs (as we know that x is beyond 50 and hence greater than 50) are the VARIABLE cost.
40 cents is the VARIABLE CHARGE per 30 min =>80 cents/$0.80 is the VARIABLE charge every hour
=> $0.8 (x-50) is the VARIABLE charge for the excess of (x-50) hours.
Hence total cost = Fixed +Variable charge for x hours
= c + 0.8(x-50) OPTION (D)
Hope this helps