Can someone explain this to me i’m having trouble

What is the value of x when x + 7 = 21?

What is the area of a triangle with a base of 7x and height of 8x expressed as a monomial? question 5 options: 1x 15x2 28x2 56x2

Fill in the blank 1. a rhombus is a rectangle a) always b) sometimes c) never 2. a square is a quadrilateral a) always b) sometimes c) never 3. a trapezoid is a kite a) always b) sometimes c) never 4. a quadrilateral is a kite a) always b) sometimes c) never 5. a square is a rhombus a) always b) sometimes c) never 6. a parallelogram is a rectangle a) always b) sometimes c) never