Write as a decimal 200 add three tens add nine hundreds

So 200 as a decimal is 200.00

add 3 tens or 3 tens 10 or 30

add 9 hundreds or 9 times 100 or 900 so

200+900+30=1130

if you mean 3 tenths in decimals or 0.3 and

9 hundreths as a demial or 0.09

added to 200 you would get

200.39

200 + 3 (.10) + 9 (.010)

200 +.30 +.09

200.30 +.09

200.39

So 200.39 is your answer ...