Behind, beside, in, out, under, on, basically anything that describes toe position of something or where something is.
The easiest way would be 6x(6x6-6)
you start with 1 and have 1 6 then 2 two 6 and 3 three 6 and so on you add a 6 for every number
Home Depot
6 - 6 + 6 - 6 + 6 - (6 / 6) = 5