Algebra: Solving for a Variable in an Exponent Classwork

1.C

$$\eqalign{2^{x+5}&=256\\2^8&=256\\\text{So....}\\x+5&=8\\-5&\;\;-5\\x&=3}$$

2.C

$$\eqalign{5^{8-y}&=125\\5^3&=125\\\text{So...}\\8-y&=3\\-8\quad&=-8\\-y&=-5\\\times-1&\;\;\times-1\\y&=5}$$

3. C

$$\eqalign{ -6^{xy}&=-216\\-6^3=216\\\text{So...}\\xy&=3}$$

4. A

$$\eqalign{ 3^{x-9}&=\dfrac{1}{243}\\3^{-5}=\dfrac{1}{243}\\\text{So....}\\x-9&=-5\\+9&\;\;+9\\x&=4}$$