Question 473019
Area = (1/2)*base*height
Let BC be the base of the triangle, Area is 90, h is height
{{{90 = (1/2)*20*h}}}
{{{90 = 10h}}}
{{{9 = h}}}
Now imagine a perpendicular line drawn straight down from A, call it point D
Then ADB makes a right triangle, where the hypotenuse is AB and one leg is h.
Now find angle ABD which is the supplement to angle B.
Using trig relationship: Sin = opp/hyp
{{{sin(ABD)= 9/15}}}
{{{ABD = sin^-1(9/15) = 36.87}}}
Angle B = 180 - ABD
{{{B = 180 - 36.87 = 143.13}}}
Therefore measure of angle B is 143.13 degrees.