hey :) i'm having problems with my little issue of calculating mileage costs.

Basically I need to work out my mielage costs for a company i'm working for
who ask that i will need to work out 40cents per mile for first 10,000 miles,
then 25 cents thereafter. eventually adding the whole lot up for one lump sum

i'm not sure how to put that in formula form.

I managed the first half of it by multiplying the overall milage by 0.4. but
how do i get it to detect when the mileage has reached 10,000 in order for it
to recalculate at 0.25?