Find the rate of change, (y2-y1)/(x2-x1), from the data given...
(2.16-1.26)/(12-7)=0.18
(1.26-0.72)/(7-4)=0.18
Since the rate is constant, this is a linear equation of the form y=mx+b. Furthermore, since 0 pencils cost 0, b=0, so the cost of the pencils is simply the number of pencils times 18 cents...
c(p)=0.18p (cost with respect to pencils is 0.18 times the number of pencils)
You would distibute first distribute
6x-10=8
add 10 on both sides
6x=18
Then you divide 6 on both sides to get x by itself so
x=3
2/3 = x/9
cross multiply and divide to find x. 9*2=18.......18/3=6. He would need 6 pints of red paint
X+x+54=180
2x+54=180
2x=126
x=63
63+54=117
one angle is 63, the other is 117