First thing first, the statement "f(x) = sqrt(x - 10) for all positive numbers x." is not an ideal GMAT statement; as this would include certain imaginary values for f (x), which GMAT never does. A rectified statement could read "f(x) = sqrt(x - 10) for all positive numbers x ≥ 10."

If f (x) = √(x - 10) then f (t) = √(t - 10)

or u = √(t - 10)

or u^2 = (t - 10)

or t = u^2 + 10.


Is it there in choices, rahul?

I guess there's a problem with this question.