-3.5x(6分之1-0.5)x7分之3÷(-2) = (-3.5) * (1/6 - 1/2) * (3/7) * (-1/2) = (7/2) * (1/6 - 1/2) * (3/7) * (1/2) = 3/4 * (1/6 - 1/2) = 3/4 * (-1/3) = -1/4