The winery sold 81 cases of wine this week. If twice as many red cases were sold than white, how many white cases were sold this week?

A 27 cases.

explanation

Let's represent the number of cases of white wine as w.
There are twice as many cases of red wine than white, so red wine = 2w.
The total number of cases is 81, so w + 2w = 81.
Solve for w:
w + 2w = 81
3w = 81
w = 27 cases.