Question

what is the equation of the following line?

Answer 1

use your 2 points and find the slope
slope(m) = (y2 - y1) / (x2 - x1)
(0,0)...x1 = 0 and y1 = 0
(15,3)...x2 = 15 and y2 = 3
now sub
slope(m) = (3 - 0) / (15 - 0)
slope(m) = 3/15
slope(m) = 1/5

now use y = mx + b
slope(m) = 1/5
use either of your points...
(0,0)...x = 0 and y = 0
now we sub
0 = 1/5(0) + b
0 = b

so your equation is : y = 1/5x + 0, or just y = 1/5x