What to do to find out what x stands for?

Jack did 3/5 of all problems on his weekend homework before sunday. on sunday he solved 1/3 of what was left and the last 4 problems. how many problems were assigned for the weekend?

The standard deviation for a set of data is 5.5. the mean is 265. what is the margin of error?

In the figure below, m∠r is 60°, and m∠t is 120°. what is m∠q? a. 60° b. 30° c. 120° d. 54