Question

A factory has a linear cost function

Answer 1

Cost function, f(x)=ax + b

If b goes up by 28 (thousands of dollars), the graph of cost function will move up by 28 in y.

Answer 2

A factory has a linear cost function, where b represents fixed costs and a represents the labor and material costs of making one item. So
y = ax + b, where y is total cost n x is no. of items

property tax is part of b so its increase will add 28 to b, the new cost function becomes:
y' = ax + b' where b' = b + 28

the line graph moves up by 28 in the y-direction