Question

Which estimate best describes the area under the curve in square units?

Answer 1

My best estimate for this figure is 15

Answer 2

see the attached figure to better understand the problem    

we know that

the estimate of the area under the curve is equal to

$Area\ estimate=Area\ of\ the\ complete\ rectangle-(Area\ triangle1\ +\ Area\ triangle 2)$

$Area\ of\ the\ complete\ rectangle=4*6=24\ units^{2}$

$Area\ triangle1=\frac{1}{2} (1.5*3)=2.25\ units^{2}$

$Area\ triangle2=\frac{1}{2} (2.5*5)=6.25\ units^{2}$

substitute the values

$Area\ estimate=24\ units^{2}-(2.25\ units^{2}+6.25\ units^{2})$

$Area\ estimate=15.5\ units^{2}$

therefore

the answer is

$15\ units^{2}$