Answer :
Answer B is correct --> y = 3.50x + 45
y represents the total cost
x represents the number of miles towed (since it costs 3.50 per one mile, that's why the variable x needs to be here because we don't know how many miles we'll have yet)
y represents the total cost
x represents the number of miles towed (since it costs 3.50 per one mile, that's why the variable x needs to be here because we don't know how many miles we'll have yet)