Answer:
In the graph we can find two points, lets select:
(2, 15) and (4, 30)
Those are the first two points.
Now, for two pairs (x1, y1) (x2, y2)
The slope of the linear equation y = s*x + b that passes trough those points is:
s = (y2 - y1)/(x2 - x1)
So the slope for our equation is
s = (30 - 15)/(4 - 2) = 15/2
then our linear equation is
y = (15/2)*x + b
now we can find b by imposing that when x = 2, y must be 15 (for the first point we selected)
15 = (15/2)*2 + b = 15 + b
b = 15 - 15 = 0
then our equation is:
y = (15/2)*x
Where we used a division and a multiplication.
