Please help ASAP with the following problem!

One side of a rectangle is 7 feet shorter than seven times the other side. find the length of the shorter side if we also know that the perimeter of the rectangle is 306 feet.

The difference between two numbers is one. three times the larger number minus two times the smaller number is 9. what are the two numbers

In a singing competition, there are 150 participants. at the end of each round, 40% of the participants are eliminated. how many participants are left after n rounds?