Iam a number betwee 60 and 100 my ones digit is two less than my tens digit i am a prime number what number am 1?

Tens digit = x 
units digit = x-2 
Number = 10x+x-2 = 11x-2 
Lowest x = 6 number 64 is not prime 
x = 7 75 is not prime 
x = 8 86 is not prime 
x = 9 97 is prime 
Answer 97

Let's name the digit: 

x- ones digit
y - tens digit

we know that x=y-2. 

Now, y can be 6,7,8,9 (the number is between 60 and 100 (so depending on your understanding of "between", 0 is also possible. but then the number would have to have -2 as its ones digit, so in any case, it's not possible). 

So the possibilities with x=y-2:

64
75
86
97
Out of those 64 and 86 are even, so they can't be prime. 
75 has 5 in its ones number: it's divisible by 5. 

so the correct answer is 97. 

The density of the cube is 40