Since the shape is a parallelogram, there are 2 pairs of opposite but equal sides --> "6a+21" and "20a+7" "11a" and "4a+7"
The easier pair is
11a = 4a+7 Subject 4a from both sides
7a = 7 Divide 7 from both sides
a = 1
A = 1
1.6m questions
2.0m answers