In a polynomial(in one variable), the greatest index of the variable is the degree of the polynomial.
Hence, the degree of
1) −3x−x4+2 [which is, −x4−3x+2] is 4.
2) 0x2+x [which is, x] is 1.
3) 14[which is, 14x0] is 0.
4) x+x2+x3+4[which is, x3+x2+x+4] is 3.