Your equation for the first point will be y=x+50
Explanation...
The x is zero so we just only put x. The y is 50 so we input a 50 giving us y=x+50.
Your equation for the second point will be y=2x+100.
Explanation...
Your slope is 2 so we input that and the y intercept is 100 giving us the equation y=2x+100.
Your equation for the third point will be y=4x+150
Explanation...
Your slope is 4 so we input that. Your y intercept is 150 so we input that. It gives us the equation y=4x+150.