Let's break down the information given in the problem:
- The shelf can hold a total of 58 cans.
- Before the shelf is full, there are still 39 cans that can be added to it.
From this information, we can set up the equation:
Let \( c \) be the number of cans already on the shelf. Since the total capacity is 58 and 39 cans can still be added, we can express the situation as:
\[ c + 39 = 58 \]
Next, we can solve for \( c \):
\[ c = 58 - 39 \] \[ c = 19 \]
So the number of cans already on the shelf is 19.
Thus, the correct equation and answer from the provided responses is:
c + 39 = 58 and 19.