I tried searching, I know this is probably straightforward, but I cant work out how to do this. Can anybody shine a light on it?
Take equation Qg gas=138,500-12,500p gas
Inverted = 11.08-0.00008Qd gas
First year algebra, my friend:
Qg =138,500 − 12,500Pg
Subtract 138,500 from both sides:
Qg − 138,500 = −12,500Pg
Divide both sides by −12,500:
(Qg/−12,500) – (138,500/−12,500) = Pg
−0.00008Qg + 11.08 = Pg
Thnaks I’m still stuggling with this bit, Iknow it should be easy, how do I get the value to insert in Qg?
Here’s another one I’m looking at?
800-4p
I understand this step -800=-4p
When I get to here -0.25+200= P I dont understand where the -0.25 comes from?
Q = 800 - 4P was the equation?
Q - 800 = - 4P
Q(1/4) - 800/4 = - P
0.25Q - 200 = - P
-0.25Q + 200 = P
You really need help on algebra 
Adam:
I agree with Harrogath: if you’re having trouble with this, you need a refresher on algebra.
Hie thee to a bookstore . . . well, those barely exist these days, so hie thee to Amazon . . . and get a copy of Algebra for Dummies.
It’ll serve you well.
Look for youtube videos that explain Algebra and Linear equations. That will also help.
Cheers guys.