Question

Suppose that the functions s and t are defined for all real numbers x as follows.

Answer 1

$s(x)=2x+4;\ D_s=\mathbb{R}\\\\t(x)=5x;\ D_t=\mathbb{R}\\\\D_s=D_t\\\\(s+t)(x)=s(x)+t(x)=2x+4+5x=7x+4\\\\(s-t)(x)=s(x)-t(x)=2x+4-5x=-3x+4\\\\(s\times t)(x)=(2x+4)\times5x=10x^2+20x$