Answer
The weight of the golf ball on Planet X is 0.173 N.
Work Step by Step
We can find the acceleration due to gravity on Planet X.
$y = \frac{1}{2}at^2$
$a = \frac{2y}{t^2} = \frac{(2)(10.0~m)}{(3.40~s)^2}$
$a = 1.73~m/s^2$
Note that the acceleration for the freely falling object is the acceleration due to gravity $g_x$ on Planet X.
$weight = mg_x = (0.100~kg)(1.73~m/s^2)$
$weight = 0.173~N$
The weight of the golf ball on Planet X is 0.173 N.