let

p = the average salary of a programmer

c = the average salary of a carpenter

the average salary for computer programmers is $7740 less than twice the average salary for carpenters:

p = 2c - 7740

combined, their average salaries are $99,000:

p + c = 99000

by solving the system of equations:

p = 2c - 7740

p + c = 99000

we find:

p = $63,420

c = $35,580

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The average salary for computer programmers is $63,420.

The average salary for carpenters is $35,580.