To figure this out, replace the variables with their given values.
p(a/b) = p(.4/.5)
Then you divide!
.4/.5 = .8
Hope this helps!
$32.072 ≈ $32.07
20% of $38 is equal to $7.60
$38 - $7.60 = $30.40
5.5% of $30.40 = 1.672
$30.40 + $1.672 = $32.072
Just do the slope of 5/3×