jmc

Multiplying out that entire polynomial would be pretty ugly, so let's see if there's a faster way. The degree of $(2x^4+3x^3+x-14)(3x^{10}-9x^7+9x^4+30)$ is the highest possible power of $x$, which occurs when we multiply $(2x^4)(3x^{10})$. This gives $6x^{14}$ so the degree of the first part is $14$. To find the degree of $(x^2+5{)}^7$, we need to find the highest possible power of $x$. This product is equivalent to multiplying $(x^2+5)$ by itself $7$ times, and each term is created by choosing either $x^2$ or $5$ from each of the seven factors. To get the largest power of $x$, we should choose $x^2$ from all seven factors, to find $(x^2{)}^7=x^{14}$ as the highest power of $x$, so the second part is also a degree-$14$ polynomial. Thus we have a degree-$14$ polynomial minus a degree-$14$ polynomial, which will give us another degree-$14$ polynomial... unless the $x^{14}$ terms cancel out. We must check this. In the first part, the coefficient on $x^{14}$ was $6$, and in the second part the coefficient was $1$. So our expression will look like $(6x^{14}+\dots )-(x^{14}+\dots )$ where all the other terms have degree less than $14$, so when simplified the expression will be $5x^{14}+\dots$. Thus the coefficient on the $x^{14}$ term is not zero, and the polynomial has degree $\boxed{14}$.