We are given that Jackson sold 15 more pounds of bananas than that of grapes, this can be written mathematically as:

Where "x" is the pounds of bananas and "y" the pounds of grapes.
We are also told that the total amount sold is $54. Using the unit price for each fruit we have the following mathematical relationship:

we get a system of two equations and two variables. The graph of the system is the following:
From the graph, we see that the point of interception is (x, y) = (27, 12). This means that the solution is 27 pounds of bananas and 12 pounds of grapes.