Write an algebraic expression of a flat rate of $25.00 and $.50 per mile

Think: slope-intercept form of the equation of a straight line: y=mx+b.

Here the "flat rate" of $25 is "b" and the "slope" of the line is $0.50/mile.

Thus, the correct algebraic expression is

y = ($0.50/mile) + $25.

0.50x+25 would be the expression form of the situation