Answer :
After substituting t = 7 in the given function, we find that d(7) = 82.6. This means that after 7 seconds, the bike has traveled 82.6 feet. Therefore, the correct answer is: A. d(7) = 82.6; after 7 seconds, the bike traveled 82.6 feet.
To find d(7), we substitute t = 7 into the function d(t) = 7.8t + 28:
[tex]\[ d(7) = 7.8(7) + 28 \][/tex]
[tex]\[ d(7) = 54.6 + 28 \][/tex]
[tex]\[ d(7) = 82.6 \][/tex]
So, the correct interpretation is: [tex]\[ d(7) = 82.6; \text{ after 7 seconds, the bike traveled 82.6 feet} \][/tex]