There are some benches in a classroom. If 4 students sit on each bench, then 3 benches are left unoccupied. However, if 3 students sit on each bench, 3 students are left standing. How many students are there in the class?

A. 36
B. 48
C. 52
D. 56
E. 64

Let the number of benches in the classroom be B, and the number of students in the classroom be S.

Step 1: Set up equations based on the given conditions.
Condition 1: If 4 students sit on each bench, 3 benches are left unoccupied.
This means the number of benches occupied is B - 3, and each bench has 4 students. Therefore, the total number of students is:
S = 4 * (B - 3) (Equation 1)

Condition 2: If 3 students sit on each bench, 3 students are left standing.
This means the number of benches occupied is B, and each bench has 3 students, plus 3 students are left standing. Therefore, the total number of students is:
S = 3 * B + 3 (Equation 2)

Step 2: Solve the system of equations.
We now have the following system of equations:

S = 4 * (B - 3)
S = 3 * B + 3
We can set these two equations equal to each other since both equal S: 4 * (B - 3) = 3 * B + 3

Step 3: Simplify and solve for B.
Expand both sides: 4B - 12 = 3B + 3

Now, subtract 3B from both sides: B - 12 = 3

Add 12 to both sides: B = 15

So, there are 15 benches in the classroom.

Step 4: Find the number of students S.
Substitute B = 15 into one of the equations, for example, Equation 2: S = 3 * 15 + 3 = 45 + 3 = 48

Therefore, there are 48 students in the classroom.

Final Answer:
The number of students in the class is 48.
So, the correct option is B. 48.