Let x=amount invested in the 11% fund then the other amount invested is 31000-x.
Although not stated, I assume the overall profit is for year’s investment.
At the end of one year, the 11% fund would gain 0.11x, while the -4% fund would lose 0.04(31000-x).
If we add these two amounts together we get 0.11x-0.04(31000-x)=0.11x-1240+0.04x, remembering that 0.04(31000-x) is a loss, which is a negative gain. The net profit is 0.15x-1240=1760, 0.15x=1760+1240=3000.
So x=3000/0.15=20000. So Susan invested 20000 in the 11% fund and 11000 in the -4% loss-making fund.