since 5.7 is a constant, lets concider it equal to K & put it aside for a moment.
now, there is an (=) sign between x & y this means there is a proportionality relation between x & y. now if we reconcider the constant, it becomes y=Kx. it means tha y is equal to K times x i.e. if we write x K times, it'll be equal to y. now we know that if we remove constants form an equation, we can relate proportionality there.... so lets remove constants;
this implies y is proportional to x.
Hope it helps.
