Question

When Lydia performed an operation on the matrix below, she forgot to include one element.

Answer 1

The operation performed by her on the given matrix is a row operation.

She multiplied the first row by 5 and then subtracted it from the second row to obtain the resultant matrix.

It can be verified by seeing that the other elements of the second row (of new matrix) follow this row operation.

$5-1*5=0\\\\-1-3*5=-16\\\\-11-5*5=-36$

So, we have that,

$b=3-2*5\\\\b=3-10\\\\b=-7$