Question 12980
Let x = Alvin's age
x+5 = Kenneth's age
x+5 + 4 = x+9 = Kenneth's age 4 yrs from now
x-5 = Alvin's age 5 years ago.


Equation:  
Product of (Kenneth 4 years from now)x (Alvin 5 years ago) = 51
(x+9)(x-5) = 51
{{{x^2+4x - 45 = 51}}}
{{{x^2 + 4x - 96 = 0}}}


Guess what!  It factors!!
{{{ (x+12)(x-8) = 0}}}
x= -12,  x= 8


An age cannot be negative, so 
x= 8 Alvin's age
x+5 = 13 Kenneth's age


Check:  In 4 years Kenneth will be 17, and 5 years ago, Alvin was 3.  The product of 17*3 is 51.
It checks.


R^2 at SCC