The current price of a non$-$dividend$-$paying biotech stock is $$140$ with a volatility of

$25\%.$ The risk$-$free rate is $4\%.$ For a three$-$month time step:

$($a$)$ What is the up movement, u$?$

$($b$)$ What is the down movement, d$?$

$($c$)$ What is the probability of an up movement in a risk$-$neutral world?

$($d$)$ What is the probability of a down movement in a risk$-$neutral world?