Eh
Did you forget to interpolate between the FL levels as well as the temp difference?
Temp is +11 at 7000 feet. It should be -1, since it's not then it's a total difference of 12 degrees.
Using values for the
ISA 8000 and 6000 you find the GPH AT 7000' to be >10.65
ISA+20 at 8000 and 6000 the GPH AT 7000 is >10.35
Interpolation between the two figures gives you a GPH of 10.47 GPH
(10.65-10.35 = .30/20 = 0.015 0.015 x 12 degrees = 0.18 subract .18 from 10.65 and you get 10.47)
Using time to destination and Fflow I find that I need 33.5 Gallons.
33.5 x 6 is 201 and 30% of 201 is 60.3 that makes it 261.3 pounds.
Now I have to add the 6 pounds and the 10 pounds and that makes it 277.3.
The answer is between 286 and 268 and so I'd probably go for answer A.
I think there's a hitch to the question though.