15%/100 = 3.51/23.40, 3.51 is your answer because multiple 100*.234 you get 23.40 and then multiply 15*.234 and get 3.51
If rounding to the hundreds
To estimate round 324 and 285 to the closest hundred.
300 - 300
Then subtract 300 - 300 =
0
If rounding to the tens
To estimate round 324 and 285 to the nearest ten.
320 - 290
Then subtract 320 - 290 =
30
The standard form is pretty much the variables on the left-hand-side and the constant alone by herself on the right-hand-side, with only positive integers on the x-variable and an integers all around.