Convert 0.81 to a fraction or simplest form

Acylinder and its dimensions are shown. which equation can be used to find v, the volume of the cylinder in cubic centimeters?

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

The linear combination method is applied to a system of equations as shown. 4(.25x + .5y = 3.75) → x + 2y = 15 (4x – 8y = 12) → x – 2y = 3 2x = 18 what is the solution of the system of equations? (1,2) (3,9) (5,5) (9,3)