Please help im confused on to how look at an equation and know

Where m is the slope of the line and b is the y-intercept of the line, or the y-coordinate of the point at which the line crosses the y-axis. to write an equation in slope-intercept form, given a graph of that equation, pick two points on the line and use them to find the slope. this is the value of m in the equation.

The method to find the female dormitory is 2-d=800

Ithink it’s b, hope this .