Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the average capacity of stadiums in the City of London that belong to schools with an enrollment less than 30,000?

### Inputs:
table_name: table, columns: ['Institution', 'Team', 'City', 'Province', 'First season', 'Head coach', 'Enrollment', 'Football stadium', 'Capacity']

### Response:
SELECT AVG Capacity FROM table WHERE City = london AND Enrollment < 30,000