3-6+12=9
Steps
you have to add first so you must add -6+12 which will be -6
Then you will take 3 - - 6 which will make it 9
Equation for company a: y=20x+8
Equation for company b: y=24x+4
Company A would be cheaper for 5 loads of laundry, because it is $108 dollars opposed to $124 which is what company b would charge for 5 loads.
$32 dollars is saved by using the services of company A instead of company B to clean 9 loads of laundry.
so the ODE is indeed exact and there is a solution of the form 
. We have
With 
, we have
so
You could divide 5 in half and then add that to the five to find the amount of flour to use in a triple recipe. Hope this helps.
