Answer:
The equation that represents Karla's sentence is 4y = y + 15
Step-by-step explanation:
From the question, 
Four times a number is equal to the number increased by 15. To write the equation that represents the sentence, we will have to use a variable to represent the unknown number. 
Since we are asked to use y for the variable, that is, let the number be y
Then 
The statement, "four times a number" will be
4×y = 4y
and this is equal to the number increased by 15, 
The number increased by 15 means y + 15.
Hence, the equation becomes 
4y = y + 15
This is the equation that represent Karla's sentence. 
If desired, 
The unknown number can be determined by solving for y in the equation
4y = y + 15
First, Collect like terms 
4y - y = 15 
3y = 15 
Then, Divide both sides by 3 
3y/3 = 15/3
y = 5 
Hence, the variable (unknown number) is 5.