Algebra practice question

Answer: B. 13

Substitute x = 3: f(3) = 6(3) − 5 = 18 − 5 = 13. Choice C (18) forgets to subtract the 5; choice D (23) mistakenly adds 5 instead of subtracting.

Why the other answers are wrong

A. 4

You added 6 and 3 instead of multiplying: 6 + 3 − 5 = 4. In 6x, the 6 multiplies x, so it's 6(3) = 18.

C. 18

You found 6(3) = 18 but stopped there — the rule subtracts 5, giving 13.

D. 23

You added the 5 instead of subtracting it: 18 + 5 = 23, but f(x) = 6x − 5 gives 18 − 5 = 13.

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