add 0+1+2+3+4 = 10
divide 10÷5 = 2
add 15+8+3+3+1 = 30
divide 30÷5 = 6
the ratio is 2:6 which simplifies to 1:3 by the means of lates per student. In other words there is one late per 3 students.
8 for 6 is the answer I think
For this case we have the following equation:

Let 
We have:

By definition, given an equation of the form 
The quadratic formula, to find the solution can be written as:

In this case we have:

Substituting in the quadratic formula we have:
See attached image
Answer:
Option B
A would be your answer. 20x-11=5x+11