Well lets try to look at the exponent x.
Exponential growth means with x going to positive infinity, y increases.
exponential decay then means the opposite, with x going to positive infinity, y decreases.
We got y = (1/6)^x
Does y increases or decreases, with an increasing x?
I guess u can answer that question urself :)
(1/6)^1 > (1/6)^2