For a linear equation, that form is "y=mx+b" where the slope "m" may then be determined by inspecting the equation (for example, in the equation "y=-2x+4" "-2" is the correct value for "m").

let 'm' represent the number of months

the information shows a total but does not identify an initial offset, so we assume zero dollars for 'b' (the x-intersection point for a standard linear equation)

these equations are valid:

100000 = 3750m + 0

200000 = 5750m + 0

of course, perhaps the problem statement intends to ask for a monthly pay that is addition to the sales total? if so, then the equations make sense and let 't' represent the total:

y = 3750m + 100000

y = 5750m + 200000

...so the system above does not produce solutions that make sense and there is most likely an error in the problem statement