Evaluate the element $a_{23}$ in the matrix A given by:

$A=([a_{11},a_{12},a_{13}],[a_{21},a_{22},a_{23}],[a_{31},a_{32},a_{33}])$

where:

$A=BC$

and:

$B=([1,2,a],[4,c,d],[7,8,e])$

and

$C=([10,13,-2],[7,f,g],[-5,11,20])$

where $a=1,c=5,d=4,e=1,f=2,g=-7$

Give your answer as an integer