Solution:

Let the number of seniors be $s.$ Then, $500-s$ people aren't seniors. We know $60\%$ of seniors don't play an instrument. Then, the number of students who don't play an instrument can be represented as $$0.3(500-s)+0.6(s) = 0.3s+150$$ and $$0.468\cdot 500=234.$$ Thus, $$0.3s+150=234$$ $$s=280.$$ This makes the number of non-seniors equal to $220.$ Since $70\%$ of non-seniors play instruments, we have the total number as $$220\cdot 0.7=154.$$

Thus, the answer is B .