The line Y = 1 is a horizontal line; its slope is zero.
A line perpendicular to Y = 1 is a vertical line.
Its slope is undefined.
(This does NOT mean that it's infinite, or anything else.
The slope of a vertical line is undefined. It doesn't have
a name or a symbol. It's nothing.)
Answer:

96 people in total.
BTW its seats and I think you meant "how many"
Answer:
a: 12 cm
b: I think it's 2.5 cm but someone might have to double check that
Step-by-step explanation:
Answer:
78
Step-by-step explanation:
13 jars/pizza
6 pizzas
13x6=78