Answer:
D=3
Step-by-step explanation:
Split this figure into 2 parts. Now you have 2 rectangles. One with sides 6 and 12. Other with sides (10 - 6) =4, and a.
Area of one rectangle is 12 × 6 = 72
Area of 2nd rectangle is 4 × a = 4a.
Since we know the total area of figure is 84
that means
72 + 4a = 84
4a = 84 - 72
4a = 12
a = 12 ÷ 4 = 3
a=3
