Value Substitution

1. The problem asks us to find the value of $10 - a$ when $a = 3$. 2. Substitute $a = 3$ into the expression: $10 - 3$. 3. Perform the subtraction: $10 - 3 = 7$. 4. Therefore, the value of $10 - a$ when $a = 3$ is $7$.