$250, at 3%, 3 years simple interest​

In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class

One number is 4 less than 3 times a second number. if 3 more than two times the first number is decreased by 2 times the second number, the result is 11. use the substitution method. what is the first number?

At noon a tank contained 10cm water. after several hours it contained 7cm of water. what is the percent decrease of water in the tank?