Explain why radiocarbon dating is not 100% accurate. What are the sources of some of this inaccuracy?

As you watch a surfer ride a wave towards the shoreline, what is the shoreline? a) displacement reference b) reference point c) coordinate plane d) cartesian boundary

Ineed to find the answer of this question because i dont understand it

Sum of brother and sisters age is 26. four times the brothers age is subtracted from three times the sisters age, the difference is 8. what are the ages of the brother and sister?