What is the answer to -3a=15

The difference of 2 numbers is 21 and the quotient of the equation is 4 then what are the two numbers?

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.

Find the value. a. 0.003 b. 0.03 c. 0.3 d. 3