With this proportion equation, I can't determine how they came up with -40 = 2x and so on. Picture below.

Question

anonymous · Answer

attachment

misty1212 · Answer

HI!!

misty1212 · Answer

they did two things at once to go from $$7x-28=9x+12$$to $$-40=2x$$

misty1212 · Answer

a) they subtracted $7x$ from both sides and 
b) they subtracted 12 from both sides

anonymous · Answer

@misty1212 why did they deduct the 7x and not the 9x?

misty1212 · Answer

it doesn't really make any difference, but since 9 is bigger than 7, when you subtract $7x$ from both sides you get $2x$ 
if they subtracted $9x$ from both sides you would have had $-2x$ with the annoying minus sign

anonymous · Answer

Thank you @misty1212. So with proportion equations, you always have the subtract the number multiplying the variable to find out what it equals?