Mathematics

A geometric progression scales by a constant ratio between consecutive terms—that's your key to unlocking this problem. Since you know two consecutive terms (the 4th and 5th), you can find that common ratio $r$ by dividing one by the other. Once you have $r$, you can use it to "step forward" from the 5th term to the 8th term, multiplying by $r$ three more times.

A geometric progression scales by a constant ratio between consecutive terms—that's your key to unlocking this problem. Since you know two consecutive terms (the 4th and 5th), you can find that common ratio $r$ by dividing one by the other. Once you have $r$, you can use it to "step forward" from the 5th term to the 8th term, multiplying by $r$ three more times.