The sum of 6 times a number and 6 is the same as the difference of the number and 9. Find the number.​

Find the solution of this system of equation -7x+y=-20 9x-3y=36

How many kilograms of a 5% salt solution and how many kilograms of a 15% salt solution must be mixed together to make 45kg of an 8% salt solution?

Frank has a devised a formula for his catering business that calculates the number of meatballs he needs to prepare. the formula is m=4a+2c, where c=number of children; m=number of meatballs; a=number of adults. how many meatballs are required for a party of 10 adults and 5 children?