I was learning about multi-dimensional integration when I came across this example.
Did the author of this example make a mistake at the second integration because the way I see it we get :
$$\int_0^1 \left[ 6xy +2xy^2 + \frac{2}{3}xy^3 + 2y\right]^3_{y=0}dx$$
$$\int_0^1 \left[ 6*3x +2x(3^2) + \frac{2}{3}x(3^3) + 2*3\right]^3_{y=0}dx$$
$$\int_0^1 \left[ 18x + 18x + 18x + 6\right]^3_{y=0}\space dx$$
$$\int_0^1 \left(44x +6\right) dx$$