Given cost function C(a) = 7.5a, where a is the number of T-shirts.
Let us complete table.
We need to plug a=1,2,3,4 in above function to get the costs to complete the table.
For a =1
C(1)= 7.5(1) = 7.50
For a =2
C(2)= 7.5(2) = 15.00
For a =3
C(3)= 7.5(3) = 22.50
For a = 4
C(4)= 7.5(1) = 30.00
In order to find the common difference we need to find the diffrences of costs 15-7.50 = 7.50
22.50-15.00=7.50.
Therefore, common difference is 7.5.
a represents the number of T-shirts.
Domain of a is the numbers we can take for a.
So, we can take value for a as 0 or greater value.
Therefore, domain for a would be a is gerater than or equal to 0.
Domain : a≥0