I have repeated this one several times, and keep getting the same answer. But it's marked wrong, can't find my error:

$\displaystyle w = xe^{\frac{y}{z}} $

$\displaystyle x = t^4 $

$\displaystyle y = 6 - t $

$\displaystyle z = 1 + 5t $

$\displaystyle \frac{dw}{dt} = e^{\frac{y}{z}}(4t^3) + xe^{\frac{y}{z}}(\frac{1}{z})(-1) + xe^{\frac{y}{z}}(\frac{-y}{z^2})(5) $

$\displaystyle \frac{dw}{dt} = e^{\frac{y}{z}}(4t^3-\frac{x}{z}-\frac{5xy}{z^2}) $

If anyone can explain what I have done wrong, I'd be extremely thankful