To write the number \( 5.1 \times 10^7 \) in decimal notation, you move the decimal point in 5.1 to the right by 7 places.
Starting with 5.1:
- Move the decimal point 1 place to the right: 51
- Move it another place to the right: 510
- Move it another place to the right: 5100
- Move it another place to the right: 51000
- Move it another place to the right: 510000
- Move it another place to the right: 5100000
- Move it one last place to the right: 51000000
After moving the decimal point 7 places to the right, you get:
51,000,000
So, \( 5.1 \times 10^7 \) in decimal notation is 51,000,000.