Need help with C homework please.

Write a function called set_byte. It is passed 3 parameters: a pointer to an unsigned long x, an index i, and a new value v for the byte.The function should change the ith byte of x to v. Byte 0 is x's least significant byte; byte 1 is the next least significant byte, etc.; byte 7 is x's most significant byte. You may only use the constants 0-255 in this function, and must restrict yourself to the the assignment operator, the dereferencing operator, multiplication, bitwise operators and shift operators.

void set_byte(unsigned long *xptr, int i, char v) {

}