Pls help me Write an equation for the following problems and then solve:
1. Five times a number added to twelve is nine times the number.
2. Twice the difference of a number and six is the sum of that number and two.
3. Four times a number is three times the difference of that number and one.

The students at jefferson middle school are raising money for a charity by selling t-shirts and hats. the number of t-shirts sold was 3 times the number of hats. the profit was $5 for each t-shirt sold and $2.50 for each hat sold. the students raised $840 for the charity. they used the system below to analyze their success and found the solution to be (144, 48). 5x+2.50y=840 x=3y how much did they earn from t-shirt sales?