What is the inverse function of f(x)=8x-5

Can someone me i’m confused. will give brainliest and a whole bunch of points

Money off coupons have been circulated to 300 households. only 2/5 of these were redeemed (used) in the local supermarket to get a free shampoo. what fraction of coupons were unused? (ps: write how you got the answer)

Use long division to indentify (12xto the second power+15x-8)divided by 3x