JEE Previous Year Question

Let $a=2i+3j+k\text{,}b=4i+j\text{,}c=i-3j-7k$ If $r=xi+yj+zk\text{,}r\cdot a=9\text{,}r\cdot b=7\text{,}r\cdot c=6$ then $\text{(}x\text{,}y\text{,}z\text{)}=$

Topic: JEE PYQ

Answer: D. Full step-by-step solution below.