How can we write the domain and range for a function that is not piece- wise such as y=x

Tanya has $42 to spend at the dolphin island store. tshirts sell for $7 each and a pair of sunglases sells for $6.tanya buys 3 tshirts. how many pairs of sunglases can she buys with the amount of money she has left

On a piece of paper graph f(x)=5•(0.4)^x

What’s 8y+48 and factor each expression completely