A developer is working with a Purchase Order automation process.

This expression is suitable for calculating the total number of boxes because it converts both strings to integers using the Convert.Tolnt32 method, which is a built-in method in .NET that can handle various formats of numeric strings1. Then, it multiplies the two integers to get the total number of boxes as an integer. The other expressions are not suitable because they either use incorrect syntax or methods that do not exist or are not reliable for converting strings to integers. References:

1: Convert.Tolnt32 Method