7x - 1 + 6x - 1 = 180
13x - 2 = 180
13x = 182
x = 14
21 sets of nachos =£52.50
56 drinks = £28
= 77 in total =£80.50
The answer is high variability
To check if a relation is a function, given a mapping diagram of the relation, use the following criterion: If each input has only one line connected to it, then the outputs are a function of the inputs.