I'm stumped on this qustion because I cant figure out a or the y intercept.

Question is...If your marginal propensity to save is always 20% and your break-even point is $10,000 then with $12,500 of disposable income, your consumption would be?

Using the consumption function formula I've got C= a + (.80)(12500). I'm stumped on how to determine a since his examples in class always gave us a. Appreciate any guidance!