Puzzle 21 Solution

Between each of the Zs there is a gap of 25 boxes, and the starting Z has an arrow pointed to the right. Labelling each box starting from the first Z to the next Z with alphabets (in the backward order), you find that the box just before the first Z ends nicely with A, so the next sequence of alphabets in backward order begins all the way until the last box.

Now, checking the boxes with numbers on them, you write down the letters corresponding to the numbers of a particular colour in their numerical order.

When you do that with black, you get the word INTEGRATE.
When you do that with blue, you get SEC X.
When you do that with red, you get WRT.
When you do that with green, you get X.

So you are able to obtain the question: Integrate sec X w.r.t. X. And the answer to this not too difficult integration is ln|sec x + tan x| + C, where C is a constant.

Answer: ln|sec x + tan x| + C