Let us assume salaries are j & k and increased ones are j+jp/100 and k+kp/100
So new salaries are say j2 & k2.
We now have two equations.
j2 = j+ jp/100
k2 = k + kp/100
Statement 1) k - j = 2000. Not Sufficient to calculate.
Statement 2) k2 - j2 = 2440. Not Sufficient to calculate.
Let us combine to the two statements :
k2 - j2 = 2440 = k+ kp/100 - ( j + jp/100)
=> ( 1 + p/100)( k - j )
=> ( 1+ p/100) * 2000
=> This is sufficient to calculate p.