1, 3, and 8 are wrong.
This site may help you.
http://www.roman-numerals.org/chart100.html
1. XVIII+XXII=35
2.VI+XIX=25
3.M-CC=900
4.LXXXIV-XLII=44
5.VI x XI=66
6.X x V x I=50
7.C/XX=5
8.XC/VI=30
4 answers
1 is 40
3 is 800
8 is 15
3 is 800
8 is 15
Now they are all right. :-)
1.
XVIII = 18
XXII = 22
XVIII + XXII = 40 = XL
2.
VI = 6
XIX = 19
VI +XIX = 6 + 9 = 25 = XXV
3.
M = 1000
CC = 200
M - CC = 1000 - 200 = 800 = DCCC
4.
LXXXIV = 84
XLII = 42
LXXXIV - XLII = 84 - 42 = 42 = XLII
5.
VI = 6
XI = 11
VI x XI = 6 * 11 = 66 = LXVI
6.
X = 10
V = 5
I = 1
X x V x I = 10 * 5 * 1 = 50 = L
7.
C = 100
XX = 20
C / XX = 100 / 20 = 5 = V
8.
XC = 90
VI = 6
XC / VI = 90 / 6 = 15 = XV
XVIII = 18
XXII = 22
XVIII + XXII = 40 = XL
2.
VI = 6
XIX = 19
VI +XIX = 6 + 9 = 25 = XXV
3.
M = 1000
CC = 200
M - CC = 1000 - 200 = 800 = DCCC
4.
LXXXIV = 84
XLII = 42
LXXXIV - XLII = 84 - 42 = 42 = XLII
5.
VI = 6
XI = 11
VI x XI = 6 * 11 = 66 = LXVI
6.
X = 10
V = 5
I = 1
X x V x I = 10 * 5 * 1 = 50 = L
7.
C = 100
XX = 20
C / XX = 100 / 20 = 5 = V
8.
XC = 90
VI = 6
XC / VI = 90 / 6 = 15 = XV