So you wont forget what you wrote and it helps you to figure out the problem. I hope this helps.
Y=mx+b where m=slope=(dy/dx) and b=y-intercept (value of y when x=0)
You have two points...(1,-2),(3,2) so
m=(y2-y1)/(x2-x1)=(2--2)/(3-1)
m=4/2=2 now that you have the slope...
y=2x+b, you can use either point to solve for the y-intercept, I'll use (3,2)
2=2(3)+b
2=6+b
b=-4 so the line is:
y=2x-4
That means the average of all data point equal:
(99+122+103+113+109+x)/6 = 103
===> (546+x)/6 = 103===> 546+x=618 & x=618-546=72, so x =72
