Jennifer works at McDonalds, and she can make 36 burgers an hour. Let h = hour. Let J = Jennifer's total
J = 36h
David, on the other hands, works at Burger King, and he makes 12 burgers an hour. Let D = David's total
D = 12h
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This time, however, Jennifer only works 2 hours. Plug in 2 for h
J = 36h; J = 36(2);
Simplify
36 x 2= 72
Jennifer makes 72 burgers in 2 hours
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David, on the other hand:
12 burgers an hour. Divide 72 with 12
72/12 = 6
David needs 6 hours to make 72 burgers
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Check: 6 hours x 12 burgers per hour = 72 total.
2 hours x 36 burgers per hour = 72 total.
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hope this helps