Exercise 1 solution (Python)

def back(bearing):
    return (bearing + 180) % 360

for b in (45, 124, 300, 180, 0, 359):
    print(b, "->", back(b))

Output:
45 -> 225
124 -> 304
300 -> 120
180 -> 0
0 -> 180
359 -> 179

Why modulo works: adding 180 always turns the bearing round. If the result is 360 or more, the % 360 wraps it back into the range 0 to 359 (the same as subtracting 360), and if it is already under 360 the % 360 leaves it unchanged. So one expression covers both "add 180" and "subtract 180".