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

### Instruction:
Which Effic is the average one that has an Avg/G larger than 3.7, and a GP-GS of 13, and a Cmp-Att-Int of 318-521-15?

### Inputs:
table_name: table, columns: ['Name', 'GP-GS', 'Effic', 'Cmp-Att-Int', 'Avg/G']

### Response:
SELECT AVG Effic FROM table WHERE Avg/G > 3.7 AND GP-GS = 13 AND Cmp-Att-Int = 318-521-15