Why is the code for Mydot incorrect?

$\%$ for symbolic declaration K x$($t$)$ y$($t$)$ Z B w t

syms K x$($t$)$ y$($t$)$ Z B w t

$\%$ Use Newton's law of motion, concepts of action and reaction, and friction to derive the equation of motion from the free b$,$

$\%$ Use the free body diagram to write the equation of motion for the top mass, m$,$ in terms of m$,$ x$,$ fs$,$ and fd$.$

Dx $=$ diff$($x$,$t$)$;

Dy $=$ diff$($y$,$t$)$;

Ft $=$ z$**$ cos$($w$*)$;

Fs $=$ K $*($x$($t$)-$y$($t$))$;

Fd $=$ B$*($Dx$-$Dy$)$;

$\%$ Use equations Fs$,$ Fd$,$ and to rewrite the equation in terms of the linear model for a spring and viscous damper.

mxdot$=-$Fs$-$Fd

Mydot$=$ Ft$+$Fs$+$Fd$+$Ky$-$BDy

Previous Assessment: $4$ of $5$ Tests Passed $(60\%)$

is Ft declared? $($Pretest$)$

is Fs Declared? $($Pretest$)$

is Fd Declared? $($Pretest$)$

is mxdot correct?

is Mydot correct?

Variable Mydot has an incorrect value.