If f(12)=4(12)-20 which function gives f(x)

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)

Arational number that is equivalent to -20/4?

How to express the radical using the imaginary unit , i.