Consider this decimal as a fraction.
We have:

We now can take the square root of the numerator and the denominator separately for a result of 16/10, or 1.6.
$40×.15=6
$40-6=$34 is the sale price
$250 x 0.25 = 62.5
62.5 + 250 == $312.50
you will pay $312.50
Area is 74 in/cm/mm^2 hope this helps :)