How do you find the equation of a line when m=75 and y intercept=-18

Since you know the slope (m is the slope) and the y-intercept, the easiest form to use is the slope-intercept form which is:    y  =  mx + b                      where  m  is the slope    and    b  is the y-intercept.

Replace  m  with  75  and  b  with  -18:

    y  =  75x  +  -18                       or                       y  =  75x  -  18

the slope of the line is enough to find the equation