math
posted by princess aimee f. santos .
i am a 9 digit number.i have 5 in my hundred thousands place.the digit in my thousands plce is 3 more than the digit in my hundred thousands place.the digit in my hundred millions place is half the digit in my thousands place.the digit in my ten millions place is the sum of the digits in my hundred millions and hundred thousands places.the rest of the digits are zerous.what number am I?

the number is abc,def,ghi
d=5 so abc,5ef,ghi
f=d+3, so abc,5e8,ghi
a=f/2=4, so 4bc,5e8,ghi
b=a+d=9, so 49c,5e8,ghi
rest=0, so 490,508,000 
write the roman numerals that comes before;
1. CDX__________
2. MMD____________ 
find the value of the missing number;
1. 48+85N39=21
2.96+15N+76=100