***WORK SHOWN***

A water faucet partially on takes 2 minutes to fill an empty sink. Opening a drain on a full sink empties the sink in 5 minutes. How long would it take for the faucet to fill the empty sink while the drain is open?

What I did was 1/2 - 1/5 = 1/x

I then found like denominators or whatever it's called, and it's 10
so I got

5/10 - 2/10 = 1/x

3/10 = 1/x

I cross multipled and got 3x = 10 which simplifies to 3.3333 BUT the answer is apparently 3.50 minutes according to this test thing. What am I doing wrong?

Question

***WORK SHOWN***

A water faucet partially on takes 2 minutes to fill an empty sink. Opening a drain on a full sink empties the sink in 5 minutes. How long would it take for the faucet to fill the empty sink while the drain is open?

What I did was 1/2 - 1/5 = 1/x

I then found like denominators or whatever it's called, and it's 10 
so I got

5/10 - 2/10 = 1/x

3/10 = 1/x

I cross multipled and got 3x = 10 which simplifies to 3.3333 BUT the answer is apparently 3.50 minutes according to this test thing. What am I doing wrong?