Answer :
Let's begin by identifying key information given to us:
[tex]\begin{gathered} a\alpha bc\Rightarrow a=kbc \\ a=kbc \\ a=10,b=5,c=15 \\ \text{Substitute these into the equation, we have:} \\ 10=k\cdot5\cdot15 \\ 10=75k\Rightarrow75k=10 \\ 75k=10 \\ k=\frac{10}{75}=\frac{2}{15} \\ k=\frac{2}{15} \\ \\ When;a=15,b=10 \\ a=kbc \\ 15=\frac{2}{15}\cdot10\cdot c \\ 15=\frac{2\cdot10}{15}c \\ 15=\frac{20}{15}c \\ 15\cdot15=20c\Rightarrow225=20c \\ 20c=225 \\ c=\frac{225}{20}=11.25 \\ c=11.25 \end{gathered}[/tex]