On number three how do u get the anser 15/4

ration?  You deserve better from your teacher.

The ratio of auditorium to theater seats is

1200:320

That's a perfectly valid answer and we could stop here if we weren't asked for lowest terms.  Here I can see that 12 and 32 have a common factor of 4 and both these end in zero so 40 is a common factor:

1200:320 = 30:8

We can keep reducing by another factor of 2,

1200:320 = 30:8 = 15:4

There's our 15/4, which we get when we write the ratio as a fraction.

15/4

This question implies a ratio is just a fraction, which it isn't.  Let's quickly note the differences.

A ratio can have zero on either side;  1:0 is a perfectly valid ratio but 1/0 is not a valid fraction.  A ratio can't be all zeros -- that's not allowed.

A ratio can have more than two numbers.  3:4:5 is a common ratio that gives rise to a right triangle.

Like fractions, ratios can be reduced:  For λ≠0,

λa : λb : λc = a:b:c

Step-by-step explanation:

subtract 710y from both sides that equals 86y

subtract 473 from both sides

that wil equal -81200

then do y=-81200/86

then you will get your answer

Hope that helps