\(a,250:\left(10-x\right)=25\\ \Rightarrow10-x=250:25\\ \Rightarrow10-x=10\\ \Rightarrow x=10-10=0\\ b,3x-2018:2=23\\ \Rightarrow3x-1009=23\\ \Rightarrow3x=23+1009\\ \Rightarrow3x=1032\\ \Rightarrow x=1032:3=344\\ c,\left(9x-21\right):3=2\\ \Rightarrow9x-21=2\times3\\ \Rightarrow9x-21=6\\ \Rightarrow9x=21+6\\ \Rightarrow9x=27\\ \Rightarrow x=27:9=3\)
\(d,53\left(9-x\right)=53\\ \Rightarrow9-x=53:53\\ \Rightarrow9-x=1\\ \Rightarrow x=9-1=8\)