You can find comprehensive solutions and step-by-step breakdowns on several educational platforms:
Don't just copy the final number. Look at the method of solution provided in the GDZ. In Ershova's manual, Level B and C tasks often require specific logical steps that teachers look for when grading.
The manual by A.P. Ershova and V.V. Goloborodko is popular because it offers for each topic, allowing students to progress from basic skills to advanced problem-solving. Where to Find Answers