Why is 3/7, and 12/21 non-proportional

If two fractions are proportional, what you do to the denominator, you must do also to the numerator.

In this case, 3/7 and 12/21 is non-proportional, because the numerator was multiplied by 4 (3 x 4 = 12) , while the denominator was multiplied by 3 (7 x 3 = 21). If it was proportional, both the numerator and denominator must be multiplied by either 3 or 4.

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7

step-by-step explanation:

the height of the surface increases from the center out to the sides of the road.

step-by-step explanation:

as we move out we move away from the x-axis.

and as mentioned in the problem statement that height of a road increases when we move away from the center x.

hence proved that 3rd option

the height of the surface increases from the center out to the sides of the road.

is the correct option.