Step 1:

Draw the related diagram:

$\"\"$

The two triangles $\"\"$ and $\"\"$ have common base $\"\"$ .

The two triangles lies between two parallel lines $\"\"$ and $\"\"$ .

The area of the $\"\"$ is $\"\"$ .

The area of the triangle $\"\"$ is $\"\"$ .

The height between the two parallel lines is always same.

The area of the $\"\"$ is $\"\"$ .

When two triangles have the common base and are between two parallel lines they have equal area.