Sn1 reaction rate comparison?

I am currently trying to solve this problem, but I cannot think of any other reason except that A is more unstable due to the tert-butyl & opposite bromide in the cis configuration due to steric effects and thus the loss of bromide is facilitated.

Compound A experiences less steric hindrance due to the trans position and therefore requires more energy to start the Sn1 reaction.

I don't know what I'm supposed to explain in detail with an energy diagram of the Sn1 reaction (it's there as a hint). For compound A, it goes from the reactant to the intermediate with a small hill at the end, and from there, with a slightly smaller hill, down to some product. For compound B, the hill from the reactant to the intermediate is a bit higher, but from the intermediate to the product, it's identical to compound A.

Am I missing something here? Perhaps something to do with the ±M effect or ±I effect?