We know that $1200 is x percent of $3800, what can be written down as:
1200 = x% * 3800
1200 = x/100 * 3800
1200 = x/1 * 38
1200 = x * 38
1200 = 38x / ÷ 38 (both sides)
x = 31,57894736842105
x ≈ 31,6 (after rounding to the nearest tenth)
So Victor pays about 31,6% of his monthly salary.