16, 24, 32, 40, 48, 56, 64, 72, etc.
The pairs are 1 and 10. 2 and 5.
Answer: 
Step-by-step explanation:
Given : The total number of cards in a deck = 52
Number of red cards = 26
There are two types of red cards : diamond and heart.
Number of diamond cards = 13
The probability that the first card is a diamond :-

Since diamond is also a red card.
Now, the total cards left = 51
The number of red cards left = 12
The probability that the second card is a red card (without repetition) is given by :-

Now, the probability of choosing a red card for the second card drawn, if the first card, drawn without replacement, was a diamond :-

Subtract 6 from both sides
15x= 195
Divide both sides by 15
x=13
Final answer: x=13
Check:
15(13)+6
195+6
201
201=201