Let us assume that the number of goals scored by Rooney, Messi and Torres before the World Cup are R, M and T respectively.
∴ R + 7 = T
and T + 8 = 2M
From Statement A:R + M = 21
By solving the equations we get the values:
R =9, M = 12 and T = 16.
From Statement B: Absolute difference between goals scored by Rooney and Messi is 3.
∴R - M = 3 or M - R = 3.
So either 'R = 21, M = 18 and T = 28’
or ‘R = 9, M = 12 and T = 16'.
We do not get a unique set of values.
Hence, the question can be answered by using Statement A alone but not by using Statement B alone.