It's also a history book.
But nowhere does the Bible say the earth is 6,000 years old - that is a figure that man deduced.
We have little idea of the true flow of time in ages past, but we do know that time is not a constant, (we're not even sure if the speed of light is a constant).
Christ did rebuild the destroyed temple in 3 days. These 3 days are three phases. The same principle of salvation from sin, addictions etc... apply.
It takes 7 phases to make man, 3 to rebuild the saved.
Deducted based on the Bible. It isn't rocket science. The Bible provides an unbroken lineage from Adam through Solomon and gives the ages of each. Solomon to the birth of Jesus was documented by the Bible and by historical records. One could quibble about how Bishop Ussher arrived at the October 23rd date but if you accept the Bible as history then it gives the age of the world at just over 6000 years.
That’s true in a sense. The Universe is expanding but the expansion rate is INCREASING with time. As you go backwards in time, the expansion rate slows.