Assuming that "piece" refers to the plywood, not the fabric. Very poorly stated
question. Rectangle 1:12 3/4 square inches = 12.75 sq in; 2 1/8 in = 2.125 in;
12.75 sq in / 2.125 in = 6 in.
Rectangle 2: 2 1/10 in = 2.1 in; 12.75 sq in / 2.1 in = 6.07143..., rounded to 6.1 in; OR 12 3/4 sq in = 51/4 sq in; 2 1/10 in = 21/10 in; 51/4 sq in / 21/10 in = 51/4 * 10/21 = 510/54 in = 85/14 in.