Here's the formulas you will need:
AFC = FC / Quantity printed
So given she prints 1,000 posters: AFC = 250.00/1000 = $0.25
Given she prints 2,000 posters: AFC = 250.00/2000 = $0.125
Given she prints 10,000 posters: AFC = 250.00/2000 = $0.025
ATC = TC / Quantity printed
where TC = FC + Variable C * Quantity printed
If she prints 1000: TC = 250 + 2000*1000 = 2,000,250
ATC = 2,000,250/1000 = 2000.25
If she prints 2000: TC = 250 + 1600*2000 = 3,200,250
ATC = 3,200,250/2000 = 1600.125
If she prints 10000: TC = 250 + 1600*2000 + 1000*8000 ($1000 for each additional poster after 2000) = 11,200,250
ATC = 11,200,250/10000 = 1120.025