let's bear in mind that a year has 12 months, so 30 months is really 30/12 years.
one pump, let's call it A, fills the reservoir by 1/60 every hour. Now, B fills it by 1/80 every hour. C empties it by 1/90 every hour. All three are on, so now we combine them into one function: t(1/60 + 1/80 - 1/90) = 1, where t = the time it takes to fill it, and 1 is just our "reservoir finally filled" marker.
isolate t onto one side and we see t = 720/13 exactly, or approximately 55.38 hours. let me know if this is the wrong answer but I'm pretty sure it is correct!
Answer for y is = 5x/2 - 17/2
$745 × 40% = $298
$745 - $298 = $447
$447 × 1/3 = $149
$447 - $149 = $298
