Suppose x is the original weight of the team which consists of y members.
And z be the weight of the new three members.
Statement 1: The average weight of the team increases by 20 kg
The equation will be, ( x * y + 3 * z) / ( y+3) = w + 20
1 Equation and 3 unknowns to solve : INSUFFICENT
Statement 2: The three new men substitute the earlier members whose weights were 64 kg, 75 kg and 66 kg.
We only have the information of the total weight ( 205 Kg) replaced but not what was added. so we cannot solve it. INSUFFICENT
Let us combine both : ( x * y - 205 + 3 * z) / ( y+3) = w + 20
Still 1 equation and 3 unknowns. Hence the Answer E.