[tex]1.\\\dfrac{3t+5}{r}=s\qquad|\cdot r\neq0\\\\3t+5=rs\qquad|-5\\\\3t=rs-5\qquad|:3\\\\\boxed{t=\dfrac{rs-5}{3}}\\\\2.\\\dfrac{2t}{r}=s\qquad|\cdot r\neq0\\\\2t=rs\qquad|:2\\\\\boxed{t=\dfrac{rs}{2}}\\\\3.\\5x+8b=2c\qquad|-8b\\\\5x=2c-8b\qquad|:5\\\\\boxed{x=\dfrac{2c-8b}{5}}\\\\4.\\\\\dfrac{7t+5}{2r}-5b=s\qquad|+5b\\\\\dfrac{7t+5}{2r}=s+5b\qquad|\cdot2r\neq0\\\\7t+5=2rs+10br\qquad|-5\\\\7t=2rs+10br-5\qquad|:7\\\\\boxed{t=\dfrac{2rs+10br-5}{7}}[/tex]