Explanation:

- The total number of students in Class A and B is 72.

- The students in A are 40% more than those in B. So, if B has X students, A has 1.4X students.

- $X+1.4X=72$ implies $2.4X=72$. Solving this gives $X=30$ students in B and 42 in A.

- Average marks of B are 50% more than A. Let A's average be Y, so B's average is $1.5Y$.

- Combined average marks are given as 58: $(42Y+45Y)/72=58$.

- Solving gives: $87Y=4176$; thus $Y=48$.

Option 4 - 48 is correct.

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