Express the area of this triangle as a monomial.
(picture below)

a. 28x^2

b. 1x

c. 11x^2

d. 14x^2

I hope this helps you

Area=height ×base/2

Area=7x.4x/2

Area =14x^2

In order to get the answer, let us analyze the given image first. 
The formula for getting the area of a triangle is A = 1/2(b*h).
So let us plug in the given values.
A = 1/2(4x)(7x)
A = 1/2 (28x2)
A = 14x^2
Therefore, the correct answer would be option D. The area of this triangle expressed in monomial is 14x^2. Hope this answer helps.