Just combine all 2y=-4
Y=-2
X=-2
Y = 1/3x
This is explained with using rise over run, as the point rises 1 time and moves over 3 times from the y intercept, hence the name. Hope this helps, and makes sense, too!
Use Pythagoras's theorem.

Now, minus 12 from 15:
15 - 12 = 3,
which you need to square.
So the length of a = 9cm.
You can also do:

Which gets 9.
Hope this helps.
The distributive property: a(b + c) = ab + ac
(-7c + 8d)0.6 = (-7c)(0.6) + (8d)(0.6) = -4.2c + 4.8d
X would be 1392. All you do is the opposite: multiplication! 87*16=1392.1392/87=16. Hope this helps! ^_^