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.
The gravity of the Moon is about one sixth that of the Earth. For example, an astronaut weighing 180 pounds on the Earth would weigh about 30 pounds on the Moon.