CONCEPT: The question tests on the basics of Rates(Arithmetic)

SOLUTION:
 

We know M1D1/W1 = M2D2/W2
(M-Number of Men | D-Number of Days & W=Total work or capacity and here it is the volume of fuel)
 Thus m*2 / g = 4 * 5 / x => x = 10 g/m (OPTION A)