Final answer:
Chen made a mistake by not properly applying the order of operations.
To find the correct value of the expression, we need to follow the order of operations and evaluate the expression step by step.
Step-by-step explanation:
The correct steps are:
-3-(-5)+(7)
-3 +5 + 7
-3 + 12
=> 9
Therefore, the correct value of the expression is 9.