Hey Aro...

first of all you have to revise the following theorem due to Thales a greek Mathematician ..

go here : Intercept theorem - Wikipedia, the free encyclopedia

in your case 3/1.8 = 3.5 /2.1 i.e 5/3 = 5/3 the ratio are the same...therefore the SEGMENTS AB and DC are parallel..and therefore the triangles ABE and ACD are similar....

the second figure reveals that angle B = angle D and angle A is common for both triangles therefore the angle c wil be equal to the angle E this ensures that these triangles are similar...

revise the similar triangles please go here Similarity (geometry) - Wikipedia, the free encyclopedia

the rest are easy....