Answer
Minor =20 and cofactor =20
Work Step by Step
The minor of an element is defined $a_{ij}$of a determinant is defined as the determinant obtained by deleting its ith row and jth columns and the minor $M$ of an element $a_{ij}$ is abbreviated as $M_{ij}$.
Further, the cofactor of an element $a_{ij}$ is abbreviated as $A_{ij}$.
where $A_{ij}=(-1)^{i+j} M$
Given: $\begin{vmatrix}5&2\\0&4\end{vmatrix}$
Here $a_{11}=5$, thus $M_{11}=$ Minor of $a_{11}=4$
Thus, $M_{11}=\begin{vmatrix}5&2\\0&4\end{vmatrix}=(5)(4)-0=20$
and
$A_{11}=(-1)^{1+1} M_{11}=(-1)^2(20)=20$