Let $t$ be TNYWR.

In last night's 75 minute choir rehearsal, Canada's Totally Musical Choir spent 6 minutes warming up, 30 minutes learning notes, $t$ minutes learning words, and the rest of the rehearsal singing their pieces. If the choir spent $N \%$ of the rehearsal singing their pieces, what is the value of $N$ ?
According to the given information, at last night's rehearsal, Canada's Totally Musical Choir (CTMC) spent $75-6-30-t=39-t$ minutes singing their pieces.

As a percentage of the full 75 minute rehearsal, this is

$$
\frac{39-t}{75} \times 100 \%=\left(\frac{4}{3}(39-t)\right) \%=\left(52-\frac{4}{3} t\right) \%
$$

Since the answer to (a) is 15 , then $t=15$ and so CTMC spent $\left(52-\frac{4}{3} t\right) \%=32 \%$ of their rehearsal singing their pieces, and so $N=32$.