The answer is 91
: O' d* {$ r- }+ \公仔箱論壇1 row 3x4+1x3=15
9 {; Q! P6 m1 i0 J$ e/ |2 row 4x5+2x4=28tvb now,tvbnow,bttvb. @. W, W4 q, v8 x( W+ b
3 row 5x6+3x5=451 a& p( U5 c+ _; N" t2 H
4 row 6x7+4x6=66tvb now,tvbnow,bttvb, S6 \1 K9 R' i! R& ^
5 row 7x8+5x7=91  |