If only the SNP would grasp the simplicity of Modern Monetary Theory or MMT they'd find it a lot easier to answer that question!

"If there’s one question a politician fears being asked, it is this one. After announcing a decision to undertake a bold new and expensive development project, the question always arises, “How are you going to pay for it?” It shouldn’t be a horror moment for politicians, but it is, and the reason is simple. They are afraid to be caught out. Such is the millstone they have tied themselves to, over the years, trying to discredit their opposition, or portray themselves as fiscally responsible. In the process, they have shot themselves in the foot because they don’t understand how sovereign money works."
https://theaimn.com