40 + 3 = 43.
If the number in the ones place is less than 5, round down, if it is more than 5 round up.
Since the number in the ones place is less than 5, 3, then we would round down and get the number 40.
If we had got for example 47, we would have rounded up to get 50.
So therefore, 40 + 3 rounded to the nearest ten is 40.
