Help I can go this far and then lost.

In planning for a new item, a manufacturer assumes that the number of items produced x and the cost in dollars C of producing these items are related by a linear equation. Projections are that 100 items will cost $10,000to produce and the 300 items will cost $22,000 to produce. Find the equation that relates C and x
Cost = K1 * n + K2
n= 100
n = 300
from here I'm lost

Well, you know the cost for each of those n.

10000=k1*100 + k2
22000=k1(300)+k2

solve for the constants.