Expert: Josh - 2/20/2006

Question
Help, 28 -6(2x +4)=124

My daughter is in 8th grade and is having problems solving this problem.  Unfortunately, I can be of no help.  She keeps ending up with a decimal?

Answer
Okay, expand the left hand side of the equation (i.e., multiply out).

28-6(2x+4)=124
28-6*(2x)-6*(4)=124
now, this line is redundant, I'm just making it clear what is being done
28-12x-24=124
4-12x=124
next, collect the integers onto the right hand side of the equation, separating the knowns (plain numbers) from the unknown (represented by "x").
-12x=124-4=120
divide both sides by -12
x=(120)/-12
answer: x=-10.

CHeck that the solution is correct by back substitution.
That is, plug in x=-10 into the original equation to see that it balances out.

Left hand side (LHS)=28 -6(2*(-10) +4)
=28-6*(-20+4)
=28-6*(-16)
=28+6*16
=28+96
=120
This is same as the right hand side of the equation, as required.