The correct answer is 58.

Solution:
Consider the given equation.
48 + 4 = – 6

To determine the missing number, first, we need to find: 48 + 4.

Which gives:
48 + 4 = 52

Then,
48 + 4 =  – 6

52 = – 6

Next, to find the missing number we find: 52 + 6.

Which gives:
52 + 6 = 58

So,

48 + 4 = 58 – 6

That is, number 58 makes the equation true.