Answer
First row solution: $\text{isotopic mass}(^{70}\text{Ga})=68.925462$
Second row solution: $0.39892$
Work Step by Step
The average atomic mass of Gallium is $69.723$, so \begin{align*}69.723&=\text{isotopic mass}(^{70}\text{Ga})\cdot 0.60108+70.9247050\cdot (1-0.60108)\\ &\Longrightarrow \text{isotopic mass}(^{70}\text{Ga})=\frac{69.723-70.9247050\cdot (1-0.60108)}{0.60108}\\ &=68.925462\end{align*}
Second row solution: $ 1 - 0.60108= 0.39892$
