As the others suggested, it’s good to turn % in $ to get a sense of proportion.
However, the same is true for the reverse. If the goal is to reduce expenses by 10m US$ and you know that total expenses are 100m US$, you should be talking about a 10% reduction in cost.
So why is this initial bit of math important (whichever direction between % and $)? It shows the interviewer that you’re not just repeating the prompt word for word (which many candidates do) but can actually think on the fly and make this problem your own.
Hence, my recommendation is always to learn how to paraphrase properly and crunch some numbers at the initial stage (if applicable) to really show that you own this!