Do aprotic solvents "slow down" SN1 reactions?


> 
> SOLVENT EFFECTS. Predict if using the polar, non-protic, solvent *N*,*N*-dimethylformamide (DMF, $\ce{Me2NC(=O)H})$ will speed up or slow down the following reactions and BRIEFLY justify your answers.
> 
> 
> **a**)  
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> [![Ph3P + CH3CH2Br](https://i.stack.imgur.com/MHGYW.png)](https://i.stack.imgur.com/MHGYW.png)
> 
> 
> **b**)  
> 
> [![Ph3P + CH3CH2OEt2 BF4](https://i.stack.imgur.com/yEUu4.png)](https://i.stack.imgur.com/yEUu4.png)
> 
> 
> 


I have no doubt that **b**) takes $\mathrm{S\_N1}$ pathway, but would DMF actually "slow down" this reaction? I want to be meticulous; I wonder if aprotic solvents "slow down" $\mathrm{S\_N1}$ reactions or just regarded as not so ideal solvents for $\mathrm{S\_N1}$ reactions. The wording of the question made me wonder.


