Jenny johnston bought some apples for 79 cents per pound and twice as many pounds of bananas for 39 cents per pound. if her total bill was $7.58, how many pounds of bananas did she buy?

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

If your asking how much altogether for 12 performance the answer will be 98,496.