A certain barrel is 1/5 full. When k liters of liquid are added to the barrel, it becomes 2/3 full. In terms of k, what is the capacity of the barrel, in liters?

GMAT QUANT Problem Solving level 600, Fractions/Ratios/Decimals
A certain barrel is 1/5 full. When k liters of liquid are added to the barrel, it becomes 2/3 full. In terms of k, what is the capacity of the barrel, in liters?

A. 3/8*k
B. 7/15*k
C. 15/7*k
D. 7/3*k
E. 8/3*k