Write an equation for each line in slope-intercept form.

y=mx+c

m= gradient(slope)

x= for you to insert an x-axis value

c= y-intercept

For this line in your graph:

y=1x+2 or y=x+2

to find m= just insert coordinates from one point to another which forms a triangle.

c= the first line that passes through the y-axis

the monthly balance will be $75,000