The math club is order tee shirts for each member. The tee shirts cost $12.50 each plus a one - time set - up fee of $25 for design on
the front and back. Write an equation that gives the total cost in terms of the number of t- shirts. Use x to represent the number of t- shirts and use y to represent the total cost. Then use the equation to find the total cost to make 126 tee shirts.

So ($25)

find out how much 126 t-shirts will cost including the $25 set up fee.  
so in calculator its (12.50 × 126) + 25. This gives you 1600. 
Now you know the answer, you work your way backwards.  

y = x + $25

Ok so since you have an initial 25 dollar fee, and 12.50 per shirt, your equation would be as follows:

y=12.50x + 25
x is representing the number of members.  
y is representing the total cost.

So for 126 shirts, just substitute for x.
Your answer would be $1,600