a
\(\overrightarrow{ v }=2 t \hat{ i }+3 t ^2 \hat{ j }\)

\(\overrightarrow{ a }=2 \hat{i}+6 t \hat{j}\)

at \(t=1, \vec{a}=2 \hat{i}+6 \hat{j}\)

\(\overrightarrow{ F }= ma =0.5(2 \hat{i}+6 \hat{j})=\hat{i}+3 \hat{j}\)

\(\overrightarrow{ F }=\hat{i}+x \hat{j} \quad \text { Hence } x=3\)