In many regions, particularly Scotland, "3C" refers to the third installment of the second level of primary mathematics (e.g., Primary Maths for Scotland ).
The search for a PDF of often leads to instructional materials or answer keys rather than the full textbook due to copyright protections. Available Resources
If a child gets a problem wrong, use a screenshot tool to copy the problem from the PDF into a blank document. Delete the numbers and create a similar problem for a second attempt.