For Tetris on Gameboy, the following equation will help you determine the score of any line you make in the game:

For a single line: (level + 1) x 4 x 10 + drop points
For a double line: (level + 1) x 4 x 25 + drop points
For a triple line: (level + 1) x 4 x 75 + drop points
For a Tetris: (level + 1) x 4 x 300 + drop points

Multiply the level you are on + 1 by 4, then multiply that by the score for the type of line (25 for double, 300 for Tetris, etc.) and add the drop points. Drop points are the number of points you get for dropping the piece from a high location. It is optional to the equation.

The scoring table for the first 9 levels is as follows (level:points):

Single:
0:40, 1:80, 2:120, 3:160, 4:200, 5:240, 6:280, 7:320, 8:360, 9:400

Double:
0:100, 1:200, 2:300, 3:400, 4:500, 5:600, 6:700, 7:800, 8:900, 9:1000

Triple:
0:300, 1:600, 2:900, 3:1200, 4:1500, 5:1800, 6:2100, 7:2400, 8:2700, 9:3000

Tetris:
0:1200, 1:2400, 2:3600, 3:4800, 4:6000, 5:7200, 6:8400, 7:9600, 8:10800, 9:12000