Please I need some answers

Suppose a pendulum is l meters long. the time, t,in seconds that it tales to swing back and forth once is given by t=2.01

Two customers went to a post office. first customer paid $12 for 14 and 5 envelopes the second paid 24.80 for 10 postcards and 15 envelopes. what is cost of each envelope?

Determine the difference: 3.2 × 1010 – 1.1 × 1010. write your answer in scientific notation.