Well we're just looking at oil paintings so let's say each shows 2 paintings...
30/2 = 15
so at most- 15 artists
If the owner is giving a free cupcake to every 4th customer. Then the easiest way to do this is to follow the 4 times table: 4, 8, 12, 16, 20
So the answer is No, Emma will not be receiving a free cupcake as she is the 17th customer and doesn't fall into the 4th customer pattern.
The simplified answer is
.
<u>Step-by-step explanation:</u>

To add or subtract denominators of the fraction must be same.
If it is not the same, we must take LCM of the denominators. and so we can add the fractions.
To make the denominator same multiply the 1st term
and 2nd term by 
= 
LCM of the denominators is 6x²+ 3xz + 2xy +yz.
Multiply the factors in the numerator.
= 
Now, the denominators are same, you can subtract it.
= 
= 
Thus the simplified solution is 