a)\(x.99+x=100\)
\(\Rightarrow x.\left(99+1\right)=100\)
\(\Rightarrow x.100=100\)
\(\Rightarrow x=1\)
b)\(420+65.x=\left(x+175\right):5+30\)
\(420+65.x=\left(x+175\right).\dfrac{1}{5}+30\)
\(420+65.x=\dfrac{1}{5}x+35+30=\dfrac{1}{5}x+65\)
\(\Rightarrow420-65=\dfrac{1}{5}x-65x\)
\(\Rightarrow-64,8x=355\)
\(\Rightarrow x=-\dfrac{1775}{324}\)
c)\(x:\left[\left(1800+600\right):30\right]=5600:\left(315-35\right)\)
\(x:80=20\Rightarrow x=20.80=1600\)
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