Let original salary be S
Then initial food expenditure was: .2S
A 10% increase in salary makes new salary: 1.1S
Since food expenditure increased by $50, new food expenditure = .2S + 50
We then get: .2(1.1S) = .2S + 50
.22S = .2S + 50
.22S - .2S = 50
.02S = 50
Original salary, or