10 percent of a number equals 40 what is the number

How do you do this geometry problem

Carson has only $20 bills and $10 bill in her wallet. the total value of the bills is $50. she has 1 more $20 bill than $10 bills. how many each kind of bill does carson have? a. one $20 and two $10 bills b. two $20 bills and one $10 bill c. one $20 bills and three $10 bills d. two $20 bills and two $10 bills

Solve for x -3+3b> 9a: ) x> 4b-9/3b: ) x< 9-4b/3c: ) x< -4b+9/-3d: ) x> 4b+9/-3