If you are looking solve for #s#:
First, multiply each side of the equation by #color(red)(t)# to isolate the #s# term while keeping the equation balanced:
#r * color(red)(t) = sqrt(s)/t * color(red)(t)#
#rt = sqrt(s)/color(red)(cancel(color(black)(t))) * cancel(color(red)(t))#
#rt = sqrt(s)#
Now, square both sides of the equation to solve for #s# while keeping the equation balanced:
#(rt)^2 = (sqrt(s))^2#
#r^2t^2 = s#
#s = r^2t^2#
If you are looking solve for #t#:
Multiply both sides of the equation by #color(red)(t)/color(blue)(r)# to solve for #t# while keeping the equation balanced:
#r * color(red)(t)/color(blue)(r) = sqrt(s)/t * color(red)(t)/color(blue)(r)#
#color(blue)(cancel(color(black)(r))) * color(red)(t)/cancel(color(blue)(r)) = sqrt(s)/color(red)(cancel(color(black)(t))) * cancel(color(red)(t))/color(blue)(r)#
#t = sqrt(s)/r#
