help!

Answer is 1 + 3 + 6 + 10 = 20.

How many positive two-digit integers are there in which each of the two digits is prime?

$\begin{array}{|c|c|c|c|c|} \hline & \mathbf{2} & \mathbf{3} & \mathbf{5} & \mathbf{7} \\ \hline \mathbf{2} & 22 & 23 & 25 & 27 \\ \hline \mathbf{3} & 32 & 33 & 35 & 37 \\ \hline \mathbf{5} & 52 & 53 & 55 & 57 \\ \hline \mathbf{7} & 72 & 73 & 75 & 77 \\ \hline \end{array}$

thank you guest and heureka!! greatly appreciated <3