Commutative property of additiona☺☺
27x - 144 + 15 = 6x - 24
27x - 129 = 6x - 24
+129 +129
--------- --------
0 105
27x = 6x + 105
-6x -6x
----- ------
21x 0
21x = 105
21x/21 = 105/21
x = 5
Remove brackets
Gather like terms
Get rid of the lone number
Transfer
Divide
Hope this helps :)
The tub holds 43 gallons.....it contains 18.....(43 - 18) = 25....so it needs 25 gallons.....after 5 minutes, the tub is full.....so it fills at a rate of 25/5 = 5 gallons per minute
y = 5x + 18....where y is the total gallons and x is the number of minutes
but we need it in standard form....
y = 5x + 18
-5x + y = 18
5x - y = -18 <== standard form