Explanation:
the slope-intercept form of a line (= linear function) is
y = ax + b
"a" is the slope of the line and represents the ratio "y coordinate change / x coordinate change" when going from one point to another on the line.
"b" is the y-intercept (the y value when x = 0; in other words, the y value where the line intercepts the y axis).
so, for the slope, let's compare 2 points. and let's pick just the first 2.
(1, 8) to (2, 11).
x changes by +1 (from 1 to 2).
y changes by +3 (from 8 to 11).
so, the slope is +3/+1 = 3/1 = 3
and our equation looks like
y = 3x + b
to get b, we use one point. I pick the first one for the smallest numbers :
8 = 3×1 + b = 3 + b
5 = b
the full line equation is therefore
y = 3x + 5