WHAT IS MATHS?give me a well known and defined explanations

Need ! give step by step solutions on how to solve number one \frac{9-2\sqrt{3} }{12+\sqrt{3} } number two x+4=\sqrt{13x-20} number three (domain and range) f(x)=2\sqrt[3]{x} +1

Diane owes $387 to her brother. if she debits her bank account $161.25 a month to pay him back, how many months will it take her to pay off the debt?

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