Create matrices $`$A$`,`$B$`$ and vector $`$d$`$ with the following code. Write codes to answer questions $3$a$-3$e$.$

$```\{$r$\}$

A $<-$ matrix$(3,4,5)$

B $<-$ matrix$($rnorm$(15),3,5)$

d $<-1$:$3$

$```$

$-**3$a$.**$ Compute the matrix multiplication $AB$^$T$ or give an explanation if there is an error, where $B$^$T$ means the transpose of matrix $B$$.$