The basic relations you need to calculate the dimensions of a truss are

shown in the attached diagram.

For a 12 degree angle, we either use a calculator or a book of tables to

get:

tan(12 degrees) ~= 0.2126

and

sin(12 degrees) ~= 0.2079.

So using the relations shown in the attachment and the dimensions from your

diagram we have:

case 1: h = 3.150 x tan(12 degrees) = 3.150 x 0.2126 = 0.6697m

case 2: h = 2.700 x tan(12 degrees) = 2.700 x 0.2126 = 0.5740m

case 3: h = 3.500 x sin(12 degrees) = 3.500 x 0.2079 = 0.7277m

RonL