Answer
$17$
Work Step by Step
You are given the following:
$a=12$
$b=7$
Since you are solving for $2a-b$ and you know the values of both variables, you can plug them in:
$2(12)-7$
Then solve, keeping in mind the order of operations. Multiplication first:
$2\times12=24$
Then subtraction:
$24-7=17$