First solve the equation:
5(3x-7)=20 => 15x - 35 = 20 => 15x = 55 => x=11/3
Fill in this solution in 6x-8:
6*11/3 - 8 = 22 - 8 = 14
Second question: apply the distributive property (ie,. both terms get multiplied by 4/5):
4/5(20x - 10) = 80/5x - 40/5 = 16x - 8