The terms are 12,7k,9,k ( terms are separated by either a plus or minus signs)
Like terms are 12 and 9, 7k and k
The coefficients are 7 and 1 ( these are numbers that come before a variable e.g 7k, so 7 is the coefficient of k.
The constants are the numbers which are not variables like 12 and 9
21 - 8k ( add or subtract the like terms only)
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