Hi Jina!
The straight road is formed by two segments (AB and BC).
Of course, if you add up the measure of the two segments you get 67 (AC).
So, set up the equation.
5x-2+2x+6 = 67
Move known terms to the right of equal with changed sign.
5x + 2x = 67 + 2 - 6
7x = 63
Divide both terms for 7
7x/7 = 63/7
x = 9
Now, we know the lenght if AB is 5x-2, and the x is 9.
5(9) - 2 = 45 - 2 = 43 miles <- answer
