Atea shop owner is mixing a blend of two teas, one of which costs $6.50 per pound, the other costing $4.00 per pound. the owner wants to have 20 pounds of a mixture that will sell for $5.50 per pound. how much of each type of tea should be used?

whatever the amounts of "x" and "y" are, they have to sum up to 20 for the mixture
thus  x + y = 20

whatever 6.50x  and 4y prices are, they must add up to (20)(5.50)
thus      

solve for "x", to see how much will be needed for the first tea type

what about the second tea type? well y = 20 - x