Question 405827
I think you want two numbers x and y such that


xy = 54
x+y = 21


Two ways to do this:


If you can factor 54 in your head, and know that 54 = 18*3, you can conclude that 18 and 3 are the numbers.


Or, letting y = 21 - x (from the second equation, we substitute and obtain a quadratic:


{{{x(21 - x) = 54}}} --> {{{-x^2 + 21x - 54 = 0}}} --> {{{x^2 - 21x + 54 = 0}}}. Either by the quadratic formula or by factoring we get x = 18 or x = 3, and both these solutions are equivalent since one implies the other.