The sum of the length, l, width, w, and depth, d, of a piece of luggage to be checked on a commercial flight cannot exceed 61 inches without incurring an additional charge.

I assume that what is being asked in this problem is the expression for the given condition that is to avoid incurring additional charge for the luggage. Adding all the dimensions should give us an answer of at most 61 inches. Mathematically expressing the condition,

l + w + d ≤ 61