Whats a branch of mathmatics that uses variables

What is the solution of sqrt x+2-15=-3

The graph shows the distance y, in inches, a pendulum moves to the right (positive displacement) and to the left (negative displacement), for a given number of seconds x. how many seconds are required for the pendulum to move from its resting position and return? enter your answer in the box.

Terri makes a quilt using three sizes of fabric squares the side lenght of each fabric square is the square root of the area