6a+13a=19a
6x-2.5x+30.5
=3.5x+30.5
8a-(5a+8)
=8a-5a-8
=3a-8
(5x+7)-(4x+0.18)
=5x+7-4x-0.18
=x+(7-0.18)
=x+6.82