Let $t$ be TNYWR.

Over the winter, Oscar counted the birds in his backyard. He counted three different types of birds: sparrows, finches and cardinals. Three-fifths of the birds that he counted were sparrows. One-quarter of the birds that he counted were finches. If Oscar counted exactly $10 t$ cardinals, how many sparrows did he count?
Suppose that Oscar saw $N$ birds in total.

From the given information, he saw $\frac{3}{5} N$ sparrows and $\frac{1}{4} N$ finches.

Therefore, he saw $N-\frac{3}{5} N-\frac{1}{4} N=N-\frac{12}{20} N-\frac{5}{20} N=\frac{3}{20} N$ cardinals.

Note that Oscar saw $\frac{3}{5} N$ sparrows and $\frac{3}{20} N$ cardinals. Since $\frac{3 / 5}{3 / 20}=4$, then he saw four times as many sparrows as cardinals.

Since he saw $10 t$ cardinals, then he saw $4 \times 10 t=40 t$ sparrows.

Since the answer to (a) is 6 , then $t=6$, and so Oscar saw $40 t=240$ sparrows.