Answer:
a. Plan C
b. Plan B
c. Between 8 and 14hrs.
Explanation:
a. Plan C = 5hrs = $200 (as plan A = $300 and cost more.)
b. Plan B = 17hrs set rate = £400
c. We see a change at 8hrs for A and then C is more value at 17hrs. So we could say 16hrs if 17hrs is wrong. But 17 Im sure will be correct as we say the word until.
I will do the rest within 12hrs, as something has come up.