PLS HELP :)) i am not sure how to solve this problem

Question

The cost of making 11 tables is $1,140. The cost of making 25 tables is $1,560. Assume this is a linear relationship.

What is the cost per table? Write a linear equation that tells you the total cost, , of making  tables:    

If your total cost is $1,590, how many tables did you make? 

Answer 1

Let we have linear function C = kn + m, C is cost, n is cost of 1 table. We have two points (11, 1140) and (25, 1560). So k = (1560 - 1140)/(25 - 11) = $30 per table.

Now C = 30n + m, m = C - 30n = 1140 - 30·11 = 810. So C = 30n + 810.

If C = 1590, then 150 = 30n + 810. n = (1590 - 810)/30 = 26 tables.