1 .
What is the coefficient of $x^{24}y^{26}$ in the expansion of $(5x - 7y)^{50}$?
(a)
${50 \choose 24} \cdot 5^{26} \cdot 7^{24}$
(b)
$- {50 \choose 26} \cdot 5^{24} \cdot 7^{26}$
(c)
${50 \choose 26} \cdot 5^{24} \cdot 7^{26}$
(d)
$- {50 \choose 24} \cdot 5^{26} \cdot 7^{24}$