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Answer:
 Ben's
Step-by-step explanation:
If E is the amount of energy that each full set of panels produces, then ...
 3 of Ismael's 5 panels produce 3/5E
 4 of Ben's 6 panels produce 4/6E
We can compare these fractions when they have a common denominator.
 3/5E = 18/30E . . . . energy from Ismael's panels
 4/6E = 20/30E . . .  energy from Ben's panels
 18/30 < 20/30 . . . . so Ben's panels are producing more energy