To solve this question, first find the slope, by taking the difference between the y variables and the X variables.
M = y2 - y1/x2 - X1 = M = 290 - 210/120 - 80
M = 80/40 = M = 2
Then using one of the points solve for b, y intercept.
Y = mx + b
210 = 2(80) + b
210 = 160 + b
b = 210 - 160 = 50.
Now plug everything together to obtain the final equation and then solve for y for 60 invites.
Y = 2x + 50
Y = 2(60) + 50
Y = 120 + 50
Y = 170.
To produce 60 invites the printer will charge $170.00.