40. A punter kicked a football with an initial velocity of 84 feet per second. The height (in feet) of the ball, \( h \), at fime \( r \) seconds is given by the function \( h(t)=-16 R+84 t+2 \) If the ball is caught by another player down the field at a height of 4 feet, how long was the ball was in the air?

How much pure acid should be mixed with 2 gallons of a \( 50 \% \) acid solution to get an \( 80 \% \) acid solution?

Câu 01: (a) Cho hàm số \( f(x)=a x^{2}-\sqrt{2} \). Tìm \( a \) biết rằng \( (f \circ f)(\sqrt{2})=-\sqrt{2} \). (b) Tìm \( m \) để hàm số \( y=\sqrt{2 x-3 m+4}-\frac{x-m}{x+m-1} \) xác định với mọi \( x>0 \).

Simplify he following fully: \( \frac{3^{3+1}-3^{-1}}{23^{x}} \) \( \frac{3^{x} \cdot 3^{1}-3^{x} \cdot 3^{-1}}{2 \cdot 3^{x}} \frac{3^{x}\left(1-\frac{1}{3}\right)}{23^{x}} \)

QUESTION 12 If \( 2^{x} 5^{y}=16 \times 125 \), where \( x \) and \( y \) are positive integers, determine \( x-y \) :

\( f(x)=5 x+6 ; g(x)=3 x-2 \) (h) Find \( \left(\left.\bar{g}\right|^{(1)}\right. \) \( \left(\frac{f}{g}\right)(1)=\square \) (Type an integer or a simplified fraction.)