Answer :
[tex]\bf \begin{array}{cccccclllll}
\textit{something}&&\textit{varies directly to}&&\textit{something else}\\ \quad \\
\textit{something}&=&{{ \textit{some value}}}&\cdot &\textit{something else}\\ \quad \\
y&=&{{ k}}&\cdot&x
&& y={{ k }}x
\end{array}\\ \quad \\
[/tex]
and also
[tex]\bf \begin{array}{llllll} \textit{something}&&\textit{varies inversely to}&\textit{something else}\\ \quad \\ \textit{something}&=&\cfrac{{{\textit{some value}}}}{}&\cfrac{}{\textit{something else}}\\ \quad \\ y&=&\cfrac{{{\textit{k}}}}{}&\cfrac{}{x} &&y=\cfrac{{{ k}}}{x} \end{array} [/tex]
now, we know that V varies directly to T and inversely to P simultaneously
thus[tex]\bf V=T\cdot \cfrac{k}{P}[/tex]
so [tex]\bf V=T\cdot \cfrac{k}{P}\qquad \begin{cases} V=42\\ T=84\\ P=8 \end{cases}\implies 42=\cfrac{84k}{8}\implies 4=k \\\\\\ V=\cfrac{4T}{P}\qquad now\quad \begin{cases} V=74\\ P=10 \end{cases}\implies 74=\cfrac{4T}{10}\implies 185=T[/tex]
and also
[tex]\bf \begin{array}{llllll} \textit{something}&&\textit{varies inversely to}&\textit{something else}\\ \quad \\ \textit{something}&=&\cfrac{{{\textit{some value}}}}{}&\cfrac{}{\textit{something else}}\\ \quad \\ y&=&\cfrac{{{\textit{k}}}}{}&\cfrac{}{x} &&y=\cfrac{{{ k}}}{x} \end{array} [/tex]
now, we know that V varies directly to T and inversely to P simultaneously
thus[tex]\bf V=T\cdot \cfrac{k}{P}[/tex]
so [tex]\bf V=T\cdot \cfrac{k}{P}\qquad \begin{cases} V=42\\ T=84\\ P=8 \end{cases}\implies 42=\cfrac{84k}{8}\implies 4=k \\\\\\ V=\cfrac{4T}{P}\qquad now\quad \begin{cases} V=74\\ P=10 \end{cases}\implies 74=\cfrac{4T}{10}\implies 185=T[/tex]