Question 575851
In order for BC to be defined, B must have 4 columns. So s = 4. This means that the resulting matrix BC is a r x 5 matrix



Matrix A is a 5 x 3 matrix. So {{{A^T}}} is a 3 x 5 matrix since the transpose flips the rows and columns.



So BC must have 5 rows in order for {{{A^T*BC}}} to be defined. This therefore means that {{{A^T*BC}}} is a 3 x 5 matrix


So the answer is choice 1)