Answer is $34$.
In first string, if we want to get $4$ as maximum length then LCS should end with either "$rr$" or "$qr$".
Only $4$ combinations are possible for LCS with length $4$:
"$qpqr$", "$qqrr$","$pqrr$","$qprr$"
Now, check for matching sequences in second string, except for "$qqrr$" all are possible.