Original saving =30% when salary =100%
When salary increased 10%,
Saving 110% × 30/100 = 33%
Saving increased = 33-30 = 3%
3%→$21
1% = $7
June salary = 110% = 110×$7 = $770

Remember that she always saves 30% of her salary.

So when her salary increased, 30% of that increase/extra amount still goes to savings.


So $21 → 30% of the increase (or 3/10)

10% (1/10) of the increase → $21 ÷ 3 = $7
100% of the increase → $7 × 10 = $70

So her salary increased by $70


Now $70 is 10%(1/10) of the original salary.

Original salary (100%) → $70 x 10 = $700


June salary = $700 + $70 = $770