Answer:
a) we know that:
the tens digit exeeds the units digit by 3, then if we have two digits
ab.
and b, the digit for units is equal to r.
then a, the digit for tens, is equal to r + 3.
Then, if r = 4, we have that the digit for tens is r + 3 = 7
and the number is 74.
b) if n is an integer, then we know that 2*n is an even number.
Now, the next even number is always 2 units away, then the next even number to 2*n is:
2*n + 2 = 2*(n + 1)
