First write 9 ten thousands out as a decimal:
0.0009
To write in scientific notation, you move the decimal point to the right of the first whole number that isn't a zero. Count the number of spaces you move the decimal:
0.0009 becomes 9 and the decimal moved 4 places to the right.
Moving the decimal to the right means the exponent needs to be a negative number, so in this case the exponent becomes -4
The scientific notation is 9 x 10^-4
