In your first question the aircraft is lighter than you think it is, so your calculated TOD, ASD and V2 will all be too high.
The wording of the options is a bit dodgy (which probably means that it is what actually appeared in a JAR exam paper), but option b is the most accurate. TOD and ASD will not really decrease, but they will be less than you expected them to be. Among other things V2 min is a function of Vsr, so your over-estimation of the weight will cause you to over-estimte V2.
In your second question you must remember that % climb gradient is approximately 100% x (Thrust - drag) / weight
This can be rewritten as
100% x (Thrust/weight - Drag/weight)... Let's call this rquation 2.
Thrust/weight is the thrust to weight ratio and the question gives this as 1 to 4, which is 1/4
The question also states that the lift to drag ratio (which is Lift/Drag) = 12/1.
If we ignore the slight change in load factor in a climb we can say taht lift = weight. This enables us to rewrite the last equation as
Weight/drag = 12/1
Turning both sides of this equation upside down gives
Drag/Weight = 1/12
So yhrust/weight = 1/4 and drag/weight = 1/12
Putting these values into equation 2 gives
% gradient = 100% x 1/4 - 1/12
This is 100% x 0.1666667 Which is about 16.7%
So we now have % gradient =