Joe drinks some milk every day. The graph shows the proportional relationship of how many liters of milk Joe drinks to number of days.
Find the amount of milk he drinks in 7 days.

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Explanation:

Draw a vertical line up from x = 7 until you reach the diagonal red line. Mark point P at this location. Then from point P, move horizontally until you reach the y axis. You should get to y = 14.

See the diagram below.

The equation of this red line is y = 2x. Whatever the input x is, we double it to get y. So if x = 7, then y = 2x = 2*7 = 14

This means that Joe drinks 14 liters of milk in 7 days. Or you could say his rate is 14 liters per week.

since both sides equal, there are infinitely many olutions.