I have been struggling with this problem for some time now, and I do not know how to approach it. Could anyone start me off? Thanks!

Consider the alcohol consumption model: a/subscript: t+1/ = a/subscript: t/ - (10.1a/subscript: t/ divided by 4.2 + a/subscript: t/) + d, where d is the constant amount that is consumed every hour. For which values of d is there an equilibrium? For which values is there no equilibrium?