A method used to find the equation of straight line is slope intercept form. The slope intercept form equation is expressed as y=mx+c (m=slope, c = y intercept). Hence, you can find the equation of straight line with slope and y-intercept using this calculator.
If the slope is 3 and c is 4, then
Equation of straight line is
y = 3x + 4
3x - y + 4 = 0