Dani is correct. The equation can be written as y = 3x+50, which is a linear equation in the form y = mx+b. We have m = 3 as the slope and b = 50 as the y intercept
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x is the number of square feet, y is the total cost in dollars
3*x or 3x repesents multiplying the cost per square foot ($3) by the number of square feet (x). For example, if you have 10 sq ft, then so far the cost would be 3*x = 3*10 = 30 dollars.
This result is then added to 50 to get the total cost. We say that 3x is the variable cost, as it changes or varies depending on how large x gets. Additionally, the 50 is the fixed cost because this cost stays the same no matter what x is
total cost = variable cost + fixed cost
y = 3x + 50
