An object's speed is 64   yards per second. What is the object's speed, in feet

Choice D is correct. Since $1$ yard is equal to $3$ feet, $64$ yards is equal to $64 \text{yards}\left(\frac{3 \text{feet}}{1 \text{yard}}\right)$, or $192$ feet. It follows that $64$ yards per second is equivalent to $192$ feet per second. Therefore, the object's speed is $192$ feet per second.

Choice A is incorrect. A speed of $61$ feet per second is equivalent to $\frac{61}{3}$, not $64$, yards per second.

Choice B is incorrect. A speed of $67$ feet per second is equivalent to $\frac{67}{3}$, not $64$, yards per second.

Choice C is incorrect. A speed of $94$ feet per second is equivalent to $\frac{94}{3}$, not $64$, yards per second.