This is an algebra problem. We let x be the variable for the number of pounds of apples bought, and y be the number of pounds of bananas bought. From the descriptions, the formulas that we can formulate are:
y = 2x --> eqn 1
0.79x + 0.39y = 7.58 --> eqn 2
Substituting eqn 1 to eqn 2:
0.79x + 0.39(2x) = 7.58
Solving for x,
x = 4.828 pounds of apples
y = 2x = 2(4.828) = 9.656 pounds of bananas bought
