What is the distance between (4,5) and (-3,0)

Need this asap if anyone can i would be very grateful. if you could show workings that would really

In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class

How many different three-digit numbers can be formed using the digits 1 comma 2 comma 9 comma 6 comma 4 comma 3 comma and 8 without repetition? for example, 664 is not allowed.