Let Marivic's age be x. Then Michelle's age is x - 5.

(This next clue is worded badly. I think this is what it means.) In three years Marivic's age is x + 3 and five years ago Michelle's age was x - 10.

Thus (x + 3)(x - 10) = 90.

x^2 - 7x - 30 = 90

x^2 - 7x - 120 = 0

(x - 15)(x + 8) = 0

So x = 15 or -8. An age of -8 is clearly ridiculous, so Marivic's present age is 15 and Michelle's present age is 15 - 5 = 10.

-Dan