Work out the HCF of 42 and 63

How can we find the measure of an exterior angle if we know the measurement of an interior angle

Pls never taught i’m really confused and i rlly need

What will be the end result for the taxpayer who filed his federal income tax return using the 1040ez form shown belowa he'll owe $173b he'll receive a refund of $173c he'll owe $3921d he'll receive a refund of $3921