import math

def b_from_correlation_formula(r_squared, std_x, std_y):
    corr = math.sqrt(r_squared)
    b_x = corr * std_y / std_x
    return b_x

def b_from_covariance_formula(r_squared, std_x, std_y):
    corr = math.sqrt(r_squared)
    cov_xy = corr * std_x * std_y
    b_x = cov_xy / (std_x ** 2)
    return b_x

method = 0
    
if method == 0:
    b_x = b_from_correlation_formula(0.4, 4, 8)
else:
    b_x = b_from_covariance_formula(0.4, 4, 8)
       

print(f'{b_x:.2f}')