[tex]\frac{\frac{7}{1}}{2}\cdota=15\\ 14a=15\\a=\frac{15}{14}\\\\b\cdot\frac{\frac{11}{2}}{3}\cdot6=b\cdot\frac{33}{2}\cdot6=b\cdot33\cdot3=99b\\\\810:a=30\\810:a=30,a\neq0\\\frac{810}{a}=30\\810=30a\\30a=810\\a=27,a\neq0\\a=27\\\\b:75=1200\\\frac{1}{75}b=1200\\b=90000\\\\630-z=515\\-z=515-630\\-z=-115\\ z=115[/tex]
