First the question is sayin that x will be substituted for -10 so for every x put -10 8(-10)=6(-10)-20
then you multiply to get the next expression so you know that 6 times -10 =-60 and you know that 8 times -10=-80 so now you have -80=-60-20 now you just solve so you would just subtract -60-20 which would equal -80 so your answer is -80=-80 which is true