Can you answer this:

Two blends of tea are mixed to make a blend that will be sold at the fair. black tea sells for $2.20 per pound and orange pekoe tea sells for $3.00 per pound. how much of each should be used to obtain a 4lb blend selling for $2.50 per pound?

Find the solution of this system of equation -7x+y=-20 9x-3y=36

45% of the trees in a park are apple trees. there are 27 apple trees in the park. how many trees are in the park in all?