Answer:
Let's define:
A = distance traveled before deploying the landing gear
B = distance traveled after deploying the landing gear.
We must have that the sum of those two distances must be equal to 600 yards.
A + B = 600 yd.
And we know that:
" the plane will travel half the distance with the landing gear than without the landing gear."
Then we have that:
B = A/2.
Now we can replace this last equation in the first one:
A + B = 600yd
A + A/2 = 600yd.
(3/2)*A = 600yd.
A = (2/3)*600yd = 400yd.
Ohama should deploy the landing gear 400 yd into the runway.