teaser.py

import numpy as np

a = np.array([[6, 0, 0], # 6 shoes
              [2, 2, 2], # 2 shoes, 2 boys, 2 whistles
              [0, 1, 3]]) # 1 boy, 3 whistles
b = np.array([30, 20, 13])
[shoe, boy, whistle] = np.linalg.solve(a,b)

print("\nshoe=", shoe, "\nboy=", boy, "\nwhistle=", whistle)
# shoe= 5.0
# boy= 1.0
# whistle= 4.0

print("shoe + boy * whistle = ", shoe + boy * whistle)
# shoe + boy * whistle =  9.0