And how to do it "manually":
7D is hexadecimal so the base is 16. If you want to convert it to base 10, the one that is normally used you do the following.
PHP Code:
A little background, in base 16 there are 16 diffrent "single" numbers after that they're combination of them so:
base 16 ~ base 10
0~0
It's normal till 9, after it the number changes to 'A' and not 10
A~10
B~11
C~12
D~13
E~14
F~15
7D = 7*16^1 + D*16^0
So in other words
7*16^1 = 7 * 16 = 112
13*16^0 = 13 * 1 = 13
x^0 is always 1
112 + 13 = 125
