4) To multiply fractions, you simply multiply the numerators together and the denominators together.

(-7/25) * (39/-14) * (50/78) = (-7 * 39 * 50) / (25 * -14 * 78)
= (-13650) / (-27300)
= 5/10
= 1/2

So, the result of multiplying these three fractions is 1/2.

5) To divide fractions, you multiply by the reciprocal of the divisor.

(6/7) - (1/7) / (-3/7) = (6/7 - 1/7) * (-7/3)
= (5/7) * (-7/3)
= -35/21
= -5/3

So, the result of this expression is -5/3.