1. XVIII+XXII=35

Question

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

Answer 1

1, 3, and 8 are wrong.

This site may help you.
http://www.roman-numerals.org/chart100.html

Answer 2

1 is 40
3 is 800
8 is 15

Answer 3

Now they are all right. :-)

Answer 4

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