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

### Instruction:
what is the cpu for the calculator with 28 kb of ram and display size 128×64 pixels 21×8 characters?

### Inputs:
table_name: table, columns: ['Calculator', 'CPU', 'RAM', 'Display Size', 'Programming Languages', 'Link Abilities', 'Year Released', 'Predecessors', 'Successors']

### Response:
SELECT CPU FROM table WHERE RAM = 28 KB of RAM AND Display Size = 128×64 pixels 21×8 characters