In the question , it is given that Jack is learning to ride a bicycle. in his first try, he rode for 4/100 mile, the second time he rode for 6/100 mile. In the next two tries, he rode successfully for 2/10 mile and 3/10 mile.
We have to find the total distance , and for that we have to add all the distances he rode, that is

Making all the denominator equal, by multiplying the last two numerators and denominators by 10

Now since the denominators are same, so we have to add the numerators, that is

In the second part, we have to find the total distance travelled in decimal , which is 0.6 miles .