TO convert a given number of base b into base 10 ,

(100)10==== 100

100, 121, 144, 202, 244, 400, ?

(121)base9 === (9^2)*1 + (9^1)*2 + (9^0)*1 == 81 + 18 + 1 =100

(144)base8 === (8^2)*1 + (8^1)*4 + (8^0)*4 == 64 + 32 + 4 =100

(202)base7 === (7^2)*2 + (7^1)*0 + (7^0)*2 == 98 + 0 + 2 =100

(244)base6=== (6^2)*2 + (6^1)*4 + (6^0)*4 == 72 + 24 +4 =100

(400)base5 === (5^2)*4 + (5^1)*0 + (5^0)*0 == 100 + 0 + 0 =100

(x)base4 === (9^2)*1 + (9^1)*2 + (9^0)*1 == 81 + 18 + 1 =100

divide 100 by 4 repeatedly and write the remainder in reverse order

```
100/4 rem==0 ;;;; 25/4 rem===1 ;;; 6/4 rem === 2 and quotient is 1 ;;; hence the answer is 1210
```