Write as a mathematical expression and solve. The sum of a number and 2 times the number is 21. Find the number. i really need help please help

3.69 (rounded)

Step-by-step explanation:

Substitute x for "a number".

New equation: x(x + 2) = 21

Distribute and combine to form a single equation: x^2 + 2x - 21 = 0

Use quadratic formula, factoring, or graphing to get all possible answers.

Quadratic formula: , where A = x^2 coefficient, B = x coefficient, and C = constant.

-5.69, 3.69

Eliminate an incorrect answer that does not line up with the above equation.

3.69

18.8 cubic inches.

step-by-step explanation:

volume of a cone = πr²h

r = 1.5 inches

h = 8 inches

pi = 3.14

volume of our cone = × 3.14 × 1.5² × 8 = 18.84 square inches

or equals to 18.8 square inches rounded up to nearest tenth.

a

step-by-step explanation: