Answer: 35 gallons
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Work Shown:
x = orange juice amount
x = (7/9)*(total amount of juice)
x = (7/9)*45
x = (7/9)*(45/1)
x = (7*45)/(9*1)
x = 315/9
x = 35 gallons of orange juice
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Another way to approach the problem:
Draw a rectangle and split it into 9 equal slips. If the whole rectangle's area is 45 square units, then each little skinny rectangle is 45/9 = 5 square units.
Shade in exactly 7 of these little rectangular slips. The shaded portion represents 7*5 = 35 square units, which corresponds to the answer of 35 gallons.