For a given function, slope is defined as the change in outputs, or y-values divided by the change in inputs, or x-values. In essence the slope asks "For a given change in x, how much does y change?" or even more simply: "How steep is the graph of this function?". This can be represented mathematically by the formula:

Since we have a table of x,y pairs it's the last form of that equation that will be the most useful to us. To compute the slope we can use any two pairs, say the first two, and plug them into our formula:

We can check this answer by using a different pair, say the last two:

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As a common sense check: Our y-values get smaller as our x-values get bigger so a negative slope makes sense.
m=-3
First, we want to find the GCF of 15 and 21, which is 3. Now we do 15 divided by 3 and 21 divided by 3, which gives us 5 and 7. To rewrite the expression, we take the GCF and put it on the outside of the parenthesis. Inside the parenthesis, we put 5 + 7. So it'll look like this:
3(5 + 7)
Answer— 45/15=3 so there is 3 classes with 15 students in each class? I didn’t really understand your question but I tried!
Hope it helped!
Subtract 15 from both sides.
28-15=13
X=13