The answer is 91
, R- ?, \. J$ I, s, z' ]/ Ltvb now,tvbnow,bttvb1 row 3x4+1x3=15: D# W$ E% I/ x
2 row 4x5+2x4=28
& ^. Z; _! P' v$ l/ d3 row 5x6+3x5=45
' K, \6 b. q7 @5 v" X- u, `5.39.217.774 row 6x7+4x6=66
1 `0 n& _+ b$ J8 H! c% D( G" W5.39.217.775 row 7x8+5x7=91  |