Hi,
Our numbers are in the decimal system (base 10), where each column as you move to the left is 10 times as much as the previous column. In the decimal system, the digits go from 0 up to 9, one less than the number system's base.
Likewise, in the hexadecimal system (base 16), each column as you move to the left is 16 times as much as the previous column. In the hexadecimal system, the digits need to go from 0 up to 15, one less than the number system's base. Since we don't have a digit to represent 10, 11, 12, 13, 14, or 15 we assign a number to represent each of those values. A = 10. B = 11. C = 12. D = 13. E = 14 and F = 15.
Columns in a hexadecimal represent 16^4, 16³, 16², 16^1 and 16^0. Those are 65536 (16^4), 4096 (16³), 256 (16²), 16 (16^1) and 1 (16^0).
So 345 base 16 is 3*256 + 4*16 + 5*1 = 768 + 64 + 5 = 837 (base 10).
D28B (base 16) is 13*4096 + 2*256 + 8*16 + 11 = 53,899 (base 10)
To convert 50,000 into hexadecimal, find the first column that is greater than 50,000 and start with the column below that. Since 16^4 is 65,536 which is too much, start with 16³ or 4096. Divide 50,000 by 4096. It goes in 12 times with a remainder of 848. For 12 a "C" will go in that column. Continue with the remainder of 848.
Now divide 848 by 16² or 256. It goes in 3 times with a remainder of 80. 3 will go in that column. Continue with the remainder of 80.
Now divide 80 by 16. It goes in 5 times with a remainder of 0. 5 will go in that column and it will be followed by a zero.
50,000 (base 10) = C350 (base 16)
I hope that helps!! :-)