#color(blue)("I am showing you the 'first principle' method upon which the")##color(blue)("'shortcut' method is based.")#
It is perfectly allowed to turn the whole thing upside down. That way you get the #t# as a numerator (the top number of a fraction).
#t/s=v/z#
Now we need to get #t# on its own on one side of the equals and everything else on the other side.
So we need to 'get rid' of the #s#. For multiply or divide we do this by changing it to 1. If it was add or subtract we would change it to 0.
Multiply both sides by #s#
#s xx t/s=v/z xx s#
This is the same as
#s/s xx t=(vs)/z#
But #s/s =1#
#1 xx t =(vs)/z#
But #1xx t = t#
#t=(vs)/z#