Help please, don’t understand this

b = -13/3

Step-by-step explanation:

Plug in the 13/3 into the t and then try to solve it. Like this:

(13/3 - 8/3)(13/3 + b) = 0 >  5/3(13/3+b) = 0 > from here you have to distribute  >  65/9 + b = 0 (here you have to subtract from both sides)

b = -65/9 (you could simplified) ---> b = -13/3