What does independent variable and dependent variable mean in math?

If a fair 6 sided cube is rolled 60 times, theoretically how many times should you expect to roll a 4 or a 5?

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling

Atown has a population of 12000 and grows at 3.5% every year. what will be the population after 7 years, to the nearest whole number?