Our school's ball last year allocated 10% of its net income to the acquisition of specialized clubs, and the remaining portion exactly covered the rental fee for the sports field. This year, we cannot issue more tickets, and the rental fee remains unchanged, so the share for the clubs could only be increased by raising the ticket price. By what percentage would the ticket price need to be increased to make the share 20%?
Last year, for every $100 \mathrm{Ft}$ of net income, $10 \mathrm{Ft}$ went to the clubs, so initially $90 \mathrm{Ft}$ was allocated for the track rental fee. In order for this year's income to cover the same rental fee and for the share to increase to $20 \%$, only $80 \%$ of the $90 \mathrm{Ft}$ track rental fee can be covered, meaning the club's share must quadruple. Thus, for every $90 \mathrm{Ft}$ track rental fee, $22.50 \mathrm{Ft}$ must go to the club, so for every $100 \mathrm{Ft}$ of last year's income, this year $112.50 \mathrm{Ft}$ must be achieved. According to this, a $12.5 \%$ increase would be necessary.