12 less than the quotient of a number and 7 is negative 2 find the number

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

Can someone plz me understand how to do these. plz, show work.in exercises 1-4, rewrite the expression in rational exponent form.[tex]\sqrt[4]{625} \sqrt[3]{512} (\sqrt[5]{4} )³ (\sqrt[4]{15} )^{7}\\ (\sqrt[3]{27} )^{2}[/tex]

A+b= 17, ab=70, find the value of |a-b|