Diagrams are isosceles, scalene, or equilateral

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Jada has a meal in a restaurant she adds up the prices listed on the menu for everything they ordered and gets a subtotal of $42.00. when the check comes, it says they also need to pay $3.99 in sales tax. what percentage of the subtotal is the sales tax

What is the perimeter of an isosceles triangle with each leg measuring 2x+3 and the base measuring 6x-2?