a)(x-2005).2006=0
=>x-2005=0
=>x=2005
b)480+45.4=(x+125):5+260
=>480+180=(x+125):5+260
=>660=(x+125):5+260
=>(x+125):5=400
=>x+125=2000
=>x=1875
c)2005.(x-2006)=2005
=>x-2006=1
=>x=2007
d){(x+50).50-50}:50=50
=>(x+50).50-50=2500
=>(x+50)*50=2550
=>x+50=51
=>x=1