Question 964106
let David's age = x
 Lauren's age = x+4
Given that  product of their ages is 45
  x*(x+4) = 45

x^2 +4*x= 45
x^2+ 4*x -45=0
x^2+9*x- 5*x-45=0
x*(x+9)- 5*(x+9)=0
(x+9)*(x-5)=0
x=-9 negative
 so x=5
Hence David's age=5
Lauren's age= 5+4=9