Question

If donald builds 32 desks how many screws will he need

Answer 1

Donald will need 32x screws.

Answer 2

Since the number of screws needed to build said desks isn't mentioned, we'll say that the value for the screws is x. Basically, you take the number of desks and multiply it by the number of screws needed for each desk.
Then we get the equation:

32(x)= The number of screws needed