To write a system of linear equations, certain words are clues to which operation to perform. In this case "additional" means "+" and "per mile" means "x", with "y" already given as "cost in dollars".
$3.00 times (x) per mile plus the initial charge $1.00 = cost in dollars
$2.00 times (x) per mile plus the initial charge $3.00 = cost in dollars
Alex 3x + 1 = y
Madeleine 2x + 3 = y
To find out the same cost, set each linear equation equal to the other.
3x + 1 = 2x + 3
Solve for x (miles) by getting x on one side of the equal sign and all the numbers on the other.
3x - 2x = 3 - 1
Combine like terms and divide each side by 1.
Answer: x = 2 miles
Then check it by substituting 2 in for x in the two original linear equations.