b = 3/4
Using point slope: y - y1 = m(x - x1).
Substitute your given slope, given point, and subsitute 0 in for x and solve for y since the y intercept is the y value when x = 0.
0.2 = 1/5, so 1/5 * 1/4 = 1/20
Therefore: y - 4/5 = 1/4(0 - 0.2) → y - 4/5 = -1/20 → y = 4/5 - 1/20 → 15/20 → 3/4