What Could It Be?

In this calculation, the box represents a missing digit. What could the digit be? What would the solution be in each case?
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative

Problem

What Could It Be? printable sheet

In the calculation below, the box represents a missing digit:

Image
What Could \It Be?


What could go in the box? What would the total be each time?

Which is the highest/lowest total?

Which totals are odd/even?