Find the measure of b

We know that the whole thing is 90 degrees, because of that little symbol.

So, b + 63 = 90
b = 90-63=27

The probability would be 1/10000.  The expected value is a loss of $9.20.

There is exactly one number to match the winning 4 digit number in 10000 possible choices.

To find the expected value, we multiply each probability by its winnings or loss:
(1/10000)*(7990) = $0.799
(9999/10000)*(-10) = $-9.999

Adding these two, we get an expected loss of $9.20.