An little brain-teaser

$3\times 4=8 \tag{1}$ $4\times 5=50\tag{2}$ $5\times 6=30\tag{3}$ $6\times 7=49\tag{4}$ $7\times 8=?\tag{5}$

After searching some time, one can see the following logic emerge : for the equations (1), (3), (4) we can see that $a\times b=\frac{ab^2}6$ . Then looking at (2) we see that $\frac{ab^2}6=4*25/6=50/3$ . Therefore the rule should be that the answer is the numerator of the fraction $a\times b=\frac{ab^2}6$ $7*8^2/6=224/3$ Hence the answer 224 .