C will let you just type in the equasion just like you have it. The compiler generates all the assembly to do the 32 bit computations. Just cast your variables into longs.
You should also check that a,b, and c don't all equal 0 at the same time or it will generate an error.
Code:
unsigned char a,b;
unsigned int c;
unsigned long d;
a = something;
b = something_else;
c = a_third_thing;
d = (55299539) / ((((long)a*100 + ((long)b)*61375 +((long)c);
the casts ((long)a) arn't really nessesary but I like to put them in to avoid any confusion.