Mark bought refreshments. sandwiches were 2.50 each and bottles of water were $1.25 each. he spent $356.25 on a total of 180 items. a. write a system of equations to model the situation. b. solve the system algebraically to find how many sandwiches and how many bottles of water mark bought.

First you have to write the equation. in the scenario, use standard form.
Ax+By=C
plug the numbers in. A=2.50, B=1.25, and C is the total, 356.25. the 180 doesn't come in quite yet.
your equation is 2.50x+1.25y=356.25. now, since they only bought 180 items, you can't go past that.

I am sorry, but I am about to leave for school, and therefore do not have enough time to answer the last of your question. I hope the part I could answer has helped you.