Help me ASAP help

I’m really confused and need your assist me with this question i’ve never been taught

Check all that apply. f is a function. f is a one-to-one function. c is a function. c is a one-to-one function.

$30 to spend on dinner tax and gratuity at mos restaurant rax is 6% and they give a 15% tip on the total bill after taxes thier dinner cost $21 which statement correctly explains wether andrew and kate have enough money to pay their bill