a)  $\underset{21}{\underbrace{XXI}}+4=25$  

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b)  $\underset{14}{\underbrace{XIV}}+9=23$  

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c)  $\underset{3}{\underbrace{III}}+17=20$  

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d)  $\underset{19}{\underbrace{XIX}}-8=11$  

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e)  $\underset{6}{\underbrace{VI}}\cdot 2=12$  

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f)  $\underset{27}{\underbrace{XXVII}}:3=9$  

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g)  $\underset{12}{\underbrace{XII}}+8=\underset{20}{\underbrace{XX}}$  

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h)  $\underset{21}{\underbrace{XXI}}:\underset{7}{\underbrace{VII}}=3$  

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i)  $\underset{9}{\underbrace{IX}}\cdot \underset{17}{\underbrace{XVII}}=153$  

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j)  $\underset{2}{\underbrace{II}}\cdot \underset{30}{\underbrace{XXX}}=60$  

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k)  $\underset{29}{\underbrace{XXIX}}-11=\underset{18}{\underbrace{XVIII}}$