$(a)$ Let $f(x,y)=x{y}^4+x^3{y}^3.$ Find

$f_x=$

$f_{}=$

$f_x=$

$f_{xy}=$

$f_{xyy}=$

$(b)$ Let $w(r,t)=e^{rt}sin(t).$ Find

$w_t=$

$w_{tr}=$

$(c)$ Let $g(r,s,t)=rln(r{s}^5{t}^3).$ Find

$g_s=$

$g_{sr}=$

$g_{srs}=$