"SELECT ALL" to see the ANSWER to the PUZZLE.

WRITE 42 x 31 as (10x4 + 2) x (10x3 + 1), Multiply It Out.

(10x4 + 2) x (10x3 + 1) = 100 x (4x3) + 10 x (4x1 + 2x3) + 1 x (2x1)

= 100 x 12 + 10 x (4 + 6) + 1 x 2

= 1200 + 100 + 2 = 1302