Multiplication is shorthand for repeated addition. So, adding $Q$ four times is $$Q+Q+Q+Q=4 \cdot Q$$ Use the same shorthand to rewrite the repeated sum $\log(8)+\log(8)+\log(8)+\log(8)=$ (hint: how many times is $\log(8)$ repeated?) So here is the big finale: $\log(8^4)=$${}\cdot\log(8)$ In general $\log(N^x)=$${}\cdot\log(N)$