Tricky maths

1. Replace The Question Mark Below With Correct Number ?

2 {38} 3
4 {1524} 5
6 {3548} 7
8 {????} 9
Ans:
6380

1st num:8*8-1=63
9*9-1=90



2. I have a role of cloth 1km long.
I have a machine which cuts this role into pieces of 10 meter long cloth.

How long would it take for the machine to cut the roll if each cut took 4 secs ?
Ans:
396 seconds

1000m would only take 99 cuts not 100.
so 4*99 => 396