remember foil and distributive property
note the invible -1
5a(2x-1)-1(8a-x)(2x-a)
look at first bit
5a(2x-a)=10ax-5a^2
2nd part
-1(8a-x)(2x-a)
-1(16ax-2x^2-8a^2+ax)
-1(17ax-2x^2-8a^2)
-17ax+2x^2+8a^2
now combine the 2 parts
10ax-5a^2-17ax+2x^2+8a^2
2x^2+3a^2-7ax
