The difference of m and 7 increased by 15 in algebra

How do you use the elimination method for this question? explain, because i really want to understand!

Hormones perform important functions within the reproductive system. during puberty, a number of changes occur in the body. which hormone is responsible for the development of these characteristics in the female? estrogen progestin progesterone testosterone

When solving a logarithm equation, how do you find the missing variable ?