The answer is 91
# J3 E( B( C' \* V1 row 3x4+1x3=15
~& E, g Q7 S" o. [: F5 I$ @! d4 Q公仔箱論壇2 row 4x5+2x4=28
! b9 m( g; h, }公仔箱論壇3 row 5x6+3x5=45tvb now,tvbnow,bttvb5 l: ^9 F# a, [1 w6 i' _6 g) ^
4 row 6x7+4x6=66
* j$ C% I' N# ?- b2 s$ ]5 row 7x8+5x7=91  |