The answer is a.
x^2 -10x+25 = x*x-2*5*x+5*5 => (x-5)(x-5)
5/6 because she already picked a blue tile. it makes the grey tile to be picked.
So the problem is asking you to combine equations, in this case the Y factor will cancel out so you will be left with the X factor and the total after you add both of the totals together,
6x-4y=16
5x+4y=6
6x-5x=x
16+6=22
x=22
I assume you are asking how much time has passed
now, we can set up a proportion with this:
let x = time(in hours)

we cross multiply to get:

divide both sides by 50 to get:

hours