Let sales in June be \(S\)
As per the question stem Income = 2000 + 10%*(S-2500) . Hence to calculate earning we need the value of \(S\)

Statement 1: Income = 20% of S
this implies 20% of S = 2000 + 10%*(S-2500) . this is a linear equation with only one unknown value \(S\), hence sufficient to find the value of S

Statement 2: Income = 15% of (S+ 17500)
this implies 15% of (S+ 17500) = 2000 + 10%*(S+17500-2500). a linear equation in \(S\). Hence the value of \(S\) can be found. Sufficient

Option \(D\)

Option D

\(2000 + (X - 2500) * 0.1 = ?\)

Stmt 1
\(2000 + (X - 2500) * 0.1 = 0.2X\)
1 equation 1 variable --> can be solved

Stmt 2
\(2000 + (X + 15000)* 0.1 = 0.15(X + 17500)\)
again, 1 equation 1 variable --> can be solved

Monthly Salary, J = 2000 + 0.1(S - 2500)
J = ?

1) 2000 + 0.1(S - 2500) = 0.2S
=> 1750 = 0.1S
=> S = 17,500
We can find the earnings in June. Sufficient.

2) 2000 + 0.1(S - 2500 + 17500) = 0.15(S + 17500)
=> S = \(\frac{875}{0.05}\)
=> S = 17,500
We can find the earnings in June. Sufficient.

D is the answer.
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