For this kind of problem it'd be better to ask, "how would we evaluate this?
The task here is EVALUATION: Finding the value of a mathematical expression.
Use Order of Operations rules. Often dubbed "PEMDAS," these rules start by emphasizing that anything enclosed inside parentheses MUST be done first. Next come mult. and di. Last are add'n and subt'n.
In 4(6/10−1/5)+0.4, we MUST combine 6/10 and -1/5 FIRST.
That's the same as 3/5-1/5, or 2/5. Then the problem looks like:
Evaluate: 4(2/5)+0.4
Now, we MUST multiply before adding or subtracting. We get
8/5 + 4/10, or 16/10+4/10 = 20/10, or 2 (answer).