Math
posted by Linda on .
1.Sally age is 12 years plus half her age. How old is she?
2.Given that: 4xy+9=0 and 3y2x=7, solve for x.

I'll answer 2.
to get rid of the y's we make this a simultaneous equation
(1)4xy=9
(2)3Y2X=7
the number of y's must be equal so that they will cancel eachother out when we add them together
so 3*(1)=12x3y=27
then we do (1)+(2)
12x3y+3y2x=27+7
hopefully you will see that the y's cancel eachother out and we are left with
10x=20
therefor x=2
if you are unsure with any of the steps feel free to ask :)