Answer:
3
Explanation:
Get rid of fractions:
Multiply the whole equation, i.e. all terms both sides of the equals sign, by the denominator or the lowest common multiple of all denominators if there are multiple fractions in the equation;
In this case, only one term is a fraction and therefore has a denominator (i.e. 7), so it is this number we multiply the equation by to get:
7(y) = 7(-³/₇.x) + 7(3)
7y = -3x + 21
3x + 7y = 21