Respuesta :
Answer:
D
Step-by-step explanation:
when you add 5.1 and 7.7 together it would be 12.8 but you have to move the decimal to the left again since it has more than one number to the left then the ^5 would turn into ^6 and 1.28x10^6 is 1,280,000 and the other is only 1,000,000