Question 74272
Let Marivic's age be x 
Let Michelle's age be y 



Marivic is five years older than Michelle 

x = y + 5 -----------------------eq. 1 


In three years, the product of her age and Michelle's age five years ago will be 90 years 

In three years marvic will be x + 3 yrs old 
Michelle's age five years ago was y - 5 yrs old 


(x + 3)(y - 5) = 90 --------------eq 2 


Substitue eq1 in eq2 

(y + 5 + 3) (y - 5) = 90 
(y + 8) (y - 5) = 90 
y^2 + 3y -40 = 90
y^2 + 3y -130 = 0


*[invoke quadratic "y", 1, 3, -130]


Answers for y= 10,-13

Age is a positive integer, so Michelle's age is 10


x = y + 5
x= 15

so Marivic's age is 15