The answer is 91
5 i6 @1 t1 Q! D( x' o! e3 K4 Sos.tvboxnow.com1 row 3x4+1x3=15
* V/ o# u1 m* A' S6 g- Ctvb now,tvbnow,bttvb2 row 4x5+2x4=28tvb now,tvbnow,bttvb6 e2 G; W! T i# ]0 \' l
3 row 5x6+3x5=457 S: }& D; l E" C. f t
4 row 6x7+4x6=66
" R8 e& M- f/ e( k, f$ i# |" I5 row 7x8+5x7=91  |