15+15+15+15=60
15 add 20 = 35
7 + 15 + 28 = 50
add 9 add 1 subtract 20 add 9 add 1
15
Add 15 to itself. Add another 15. Keep adding 15. Multiples are multiple additions.
They add up to 7/15 pus 2/15 = 9/15 or 3/5 in its simplest form
12+9=21 21+15=36 36+13=49 49+6=55
19
15
-13
30