Answer: 15, because it is 16-1
Let C present amount of change
The expression is C = 50 - d
Well, if you subtract one you get -1=log4^x. base four on each side: 4(to the power of negative 1)=4(to the power of log base four) x. Four to the power of log base 4 cancels, and you're left with 4 to the power of -1=x. the negative exponent recipricates, so x=1/4. you're welcome.
