Answer
The unknown angle is 145$^{\circ}$.
Work Step by Step
The sum of the angle in a Triangle is 180∘.
Here we will solve for the unknown angle. We will label it X.
Therefore:
180$^{\circ}$ = 20$^{\circ}$ + 15$^{\circ}$ + X
X = 180$^{\circ}$ - (20$^{\circ}$ + 15$^{\circ}$)
X = 180$^{\circ}$ - (35$^{\circ}$)
X = 145$^{\circ}$
