The equation that gives the relationship between cost (c) and area (a) is c = 2a
A variation is a relation between a set of values of one variable and a set of values of other variables
Given that: the cost (c) to paint a building varies directly with the area of the surface being painted (a) in square feet
We can write:
c α a
c = ka
where k is the constant of proportionality
since c = $3,000 and a = 1500
c = ka
3000 = 1500k
k = 3000/1500
k = 2
Thus, the equation of the relationship is c = 2a
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