How many grams are in one serving? Ok so this is all the information your getting in the question I have a tip if your teacher lets you do this out a "?" By the question and say I don't know sorry I don't know this
3y + 9x = 12
3y = -9x + 12
y = -3x + 4
If you want function notation you can replace y with f(x)
f(x) = -3x + 4
You worked 5:15. From 6:45 to 12 is 5:15 then as you finish at 12:30 you just have to add 30 minutes to 5:15