In this equation we can see that there is only one unknown factor and that is x. So one equation is enough. If there were two unknown factors, then two equations would have been required to find them. Now coming back to the equation
6/16 = 9/x
6 * x = 9 * 16
6x = 144
x = 144/6
= 24
This is the only way to simplify the equation and get the
desired result and that is finding the value of x.
