Answer:
x = 3
Step-by-step explanation:
[tex] (3x,\: x +1)=(x_1, \:y_1) [/tex]
[tex] (11,\: 12)=(x_2, \:y_2) [/tex]
[tex]slope = \frac{y_2 - y_1}{x_2 - x_1} \\ \\ 4 = \frac{12 - (x + 1)}{11 - 3x} \\ \\ 4 = \frac{12 - x - 1}{11 - 3x} \\ \\ 4 = \frac{11 - x}{11 - 3x} \\ \\ 4(11 - 3x) = 11 - x \\ \\ 44 - 12x = 11 - x \\ \\ 44 - 11 = 12x - x \\ \\ 33 = 11x \\ \\ x = \frac{33}{11} \\ \\ \huge \red{ \boxed{x = 3}}[/tex]
