Explanation:
m = n + x/p
to make x the subject means to transform this into an equation, where we have x alone on one side being expressed by the other terms.
e.g.
x = ...
remember, when we change one side of an equation, we have to do the same thing to the other side as well. otherwise the equation relation is broken. it is like a balance that we need to keep in balance.
so,
m = n + x/p | subtract n from both sides
m - n = x/p | multiply both sides by p
(m - n)p = x
or
x = (m - n)p
because it is an essential property of an equation relation that
a = b means that also b = a