Answer:
The first: 2 < x < 3
Step-by-step explanation:
[tex]3x+4\geq13\\\\3x\geq9\\\\x\geq3\\\\A=\big<3\,,\ \infty)[/tex] [tex]\frac12x+3\leq4\\\\\frac12x\leq1\\\\x\leq2\\\\B=(-\infty\,,\ 2\big>[/tex]
[tex]A\cup B\not=\varnothing\quad for\ all\ x\in(-\infty\,, 2\big>\cup\big<3\,,\ \infty)[/tex]
so:
[tex]A\cup B=\varnothing\quad for\ x\in(\,2\,,\ 3\,)[/tex]
