A road construction company charges 125 million dollars for constructing a 20km stretch of highway and 245 million dollars for constructing 40 km of similar highway. Based on these costs and assuming a linear relationship exists between the total cost and the length of road constructed,

Determine the cost constructing: a) 25 km of similar highway,
b) 52km of similar highway

Question

A road construction company charges 125 million dollars for constructing a 20km stretch of highway and 245 million dollars for constructing 40 km of similar highway. Based on these costs and assuming a linear relationship exists between the total cost and the length of road constructed, 

Determine the cost constructing: a) 25 km of similar highway, 
b) 52km of similar highway

whpalmer4 · Answer

Think of this as points on a line, with one point being (20,125) and the other (40,245) 

I put them in this order because the distance is clearly the independent variable, and the cost is the dependent variable.

Find the equation of the line that goes through those points.  Then you can calculate the cost of the other lengths by substituting them in to the formula as $x=25$ and $x=52$.