Answer:
C(x)= 19x+1260
Step-by-step explanation:
For 90 sweatshirts
2970=90a+b
For 280 sweatshirts
6580=280a+b
Subtracting equation 1 from 2 then
6580-2970= (280x-90x)+b-b
3610=190a
x=3610/190=19
2970=90(19)+b
b=2970-90(19)=1260
Therefore, the equation will be
C(x)= 19x+1260