To solve the equation 1/3 + 2/3 : x = -7, we need to follow these steps:

1. Simplify the expression on the left side of the equation.
1/3 + 2/3 : x = -7
1/3 + (2/3) / x = -7

2. Simplify the division on the left side by multiplying the numerator by the reciprocal of the denominator.
1/3 + (2/3) * (1/x) = -7
1/3 + 2/3x = -7

3. Combine the fractions on the left side by finding a common denominator.
(1 + 2/3x) / 3 = -7

4. Multiply both sides of the equation by 3 to eliminate the fraction.
1 + 2/3x = -21

5. Subtract 1 from both sides of the equation.
2/3x = -22

6. Multiply both sides of the equation by 3/2 to solve for x.
(2/3x) * (3/2) = -22 * (3/2)
x = -33