А)2a+4/a+2*5/2=2(a+2)*5/(a+2)*2=5
б) 4a^2/2a-b/12a^3/4a^2-b^2/2a^2/6a^2-3ab=
1)4a^2/2a-b/12a^3/(2a-b)(2a+b)=4a^2*(2a-b)(2a+b)/(2a-b)*12a^3=2a+b/3a
2)2a+b/3a:2a^2/6a(a-2b)=2a+b*6a(a-2b)/3a*2a^2=(2a+b)(a-2b)/a^2
в) (1-a+3b/2a)*(1/a+3b+1/(a+3b)
1)1-a+3b/2a=2a-a+3b/2a=a+3b/2a
2)1/a+3b+1/a+3b=1/(a+3b)^2
3)(a+3b)*1/2a*(a+3b)^2=1/2a(a+3b)
Вроде так)