Which of the following values of x makes the rational expression below undefined? x-25/x+13 a. 13 b. 0 c. 25 d. -13

X-25 / x + 13
 For this case what you should know is that an indefinite expression are those in which mathematically no numerical value can be obtained.
 We have then that a division between zero causes an expression to be undefined.
 For x = -13 we have:
 (-13-25) / (- 13 + 13) = - 38/0 (undefined)
 
 x = -13
 d. -13

6(2x + 5y)6 (2x) = 12x6 (5y) = 30y12x + 30y