So given the values on the number line, AB and BC, adding them together will get the length of AC. If AB equals [tex]x-3[/tex] and BC equals [tex]5[/tex], the value of AC should be [tex]x-3+5[/tex]. Since you are given the length of AC, [tex]21[/tex], you can create an equation to solve for x. This equation would be [tex]x-3+5=21[/tex]. Isolating the x on the left (or right hand side) gets the value of x to be 19. The same thing goes for the 2nd question.
