"approx. around 750 to 800 sq. feet of his garage for business use as well, (~95% business use"

The space is supposed to be 100% business use, not overlapping. You will only report the amount of sf used solely for business, not a shared space.

You report the Office space, as sf used 100% for business. The same is true of the garage. it isn't "95% of the garage" or 95% of some part of the garage. It is somewhere around 700 sf of the garage is 100% business (95% of the sf range you gave, at the lower end). Do the math:

If I have a 1,000 sf garage and use one corner and one half, I would measure each space that is exclusively business and add that sf together; not projecting that this entire garage is X% business.