Let S be the number of students going on the trip, and let C be the cost per student.

So then we can get one equation

Now we can use the rest of the info to write another equation

we know that four less students are going so thats S-4 and that it will cost two dollars more per student C+2 and this still needs to equal the cost of the trip. So we get

Now we can isolate a variable from the first equation to get

and sub this into the 2nd equationt to get

Reducing gives

Now multiply the equation by C to clear the fractions and get

So C is 10 or -12 Since the cost shouldn't be negative. I wish someone would pay me to go to a museum C is 10. Plugging back into the first equation we get S=24.

I hope this helps. Good luck.