Answer:
77
Step-by-step explanation:
Substitution pretty much involves replacing a value (in this case, the letter x) with another value (from the set).
To make 3x = 231 true, we have to replace x with each element in the set and see if the equation holds.
{77, 78, 79}
77
3(77) = 231 This is correct
78
3(78) = 234 This is incorrect!
79
3(79) = 237 This is incorrect!
