You can put this solution on YOUR website! if karens age is x, and we know that karen is seans age + 5 lets form an equation.
let seans age be y such that y + 5 = x
if y * (y + 5) = 300 find the value of x
solve for y first
y^2 + 5y = 300
we now have a quadratic equation
y^2 + 5y - 300 = 0
You can solve it using any of the known methods: perhaps the easiest here would be the quadratic formula.
a = 1; b = +5; c = -300
the result will be the roots -20 and 15; since age can't be less than 0 we can discard the first root.
so seans age is 15 and therefore karens age is 15+5 = 20 years