a)
[tex]s = \frac{a+2t}{3} \ \ \ |\cdot 3\\\\3s = a+2t \ \ \ |-a\\\\3s-a = 2t \ \ \ |:2\\\\\boxed{t = \frac{3s-a}{2}}[/tex]
b)
[tex]F = \frac{4y-x}{3} \ \ \ |\cdot 3\\\\3F = 4y-x \ \ \ |+x\\\\3F+x = 4y \ \ \ |-3F\\\\\boxed{x = 4y-3F}[/tex]
c)
[tex]P =t -3rt+2 \ \ \ |+3rt\\\\P+3rt =2 \ \ \ |-P\\\\3rt = 2-P \ \ \ |:3t\\\\\boxed{r = \frac{2-P}{3t}}[/tex]
d)
[tex]a = \frac{4k-l}{m}+2 \ \ \ |\cdot m\\\\am = 4k-l + 2m \ \ \ |+l\\\\am+l = 4k+2m \ \ \ |-am\\\\l = 4k+2m-am\\\\\boxed{l = 4k+m(2-a)}[/tex]
