Alandscaping company needs 220 gallons of 29% fertilizer to fertilize the shrubs in an office park. they have in stock 35% fertilizer and 25% fertilizer. how much of each type should they mix together?

Let 
x> volume of 35% fertilizer
y> volume of 25% fertilizer

we know that
x+y=220> x=220-y> equation 1
x*0.35+y*.25=220*.29> equation 2

substitute equation 1 in equation 2
[220-y]*0.35+0.25*y=63.8> 77-0.35*y+0.25*y=63.8
0.10*y=13.2> y=13.2/0.10> y=132 gal
x=220-y> x=220-132> x=88 gal

the answer is
88 gal of 35% fertilizer
132 gal 25% fertilizer