How do I do these statistical studies? Can't tell which one is which.

Factor the expression using the gcf. the expression 21m−49n factored using the gcf

Arectangle has a width of 5 cm and a length of 10 cm. if the width is increased by 3, how does the perimeter change?

Let event a = you roll an even number on the first cube.let event b = you roll a 6 on the second cube.are the events independent or dependent? why?