I couldn't figure out how to solve these two problems and have to show ALL my work for both, if someone could help me I would appreciate it thanks!

1. The perimeter of a rectangular field is 300 meters. This field is to be fenced along three sides only. The fencing along it's two lengths and one width is to be done at $50 per meter. If the total cost of the fencing is $12,000, what are the field's dimensions?

2. The admission fee at a fair is $2 for children and $4 for adults. On a certain day, 2,000 people enter the fair and $6,000 is collected. How many children and how many adults went to see the fair on that day?