So basically when you are adding or subtracting fractions the denominators the number on the bottom of the fraction 12 in this case and 8 as well the two denominators sharing the least common multiple so what is the lowest multiple of 12 and 8 so count off 12: 12, 24, 36... 8: 8, 16 , 24 does that help?
It will take under 10 seconds to hit the ground
Multiply 13 by the 2 above the divide line
13*2 = 26
so the number in the box should be 260
