把6a+13a 6x-28-2.5x+30.5 8a-(5a+8) (5x+7)-(4x+0.18）这几个算试如何化简?

6a+13a=19a
6x-28-2.5x+30.5=3.5x+2.5
8a-(5a+8)=8a-5a-8=3a-8
(5x+7)-(4x+0.18)=5x+7-4x-0.18=x+6.82看不懂，回答清楚。用递等式第一题6a+13a=19a 第二题6x-28-2.5x+30.5=3.5x+2.5第三题8a-(5a+8)=8a-5a-8=3a-8第四题(5x+7)-(4x+0.18)=5x+7-4x-0.18=x+6.82