between which two digits should a decimal point be placed so the value of the resulting number is 8.7654321 x 10^4 ?

Answer 1

8 x 10,000 is 80,000

so put the decimal between 4 and 3

Answer 2

Right. All you need to do is look at your exponent. Positive tells us to move that many spaces to the right, and negative tells us to move that many spaces to the left. Positive four tells us to move it four to the right, which is between the four and three.