X( 1+ 10%)+(7200-X)80% = 7200

Get x = 4800,7200-x = 2400.

Original expenditure: 4800*80+7200*700=5424000.

Funds to be used now: 4800 *1.1* 80+7200 * 0.8 * 700 = 4454400.

The area that can be afforested with the remaining funds is (5424000-4454400)/300=3232 square meters.