I usually skip the calculus but here goes
[tex]\sin y = 5x^4 - 5[/tex]
Taking derivatives with respect to x,
[tex]\dfrac{ d (\sin y)}{dx} = \dfrac{ d(5x^4 - 5)}{dx}[/tex]
[tex]\cos y \dfrac {dy}{dx} = 20 x^3[/tex]
[tex]\dfrac {dy}{dx} = \dfrac{ 20 x^3}{\cos y}[/tex]
At [tex](x,y)=(1,\pi)[/tex] we get
[tex]\dfrac {dy}{dx} = \dfrac{ 20 (1)^3}{\cos \pi} = -20[/tex]
Answer: -20
