We know that this triangle is isosceles because of the congruent markings on the side lengths. The definition of an isosceles triangle states that if two sides are congruent, two angles must also be congruent.
We can write our current expression as:
45 + x + x = 180
A triangle's angles must add up to 180.
Since we know that the two remaining angles must be the same measure, we can write the expression as:
45 + x(2) = 180
From here, we can use inverse operations to solve.
Firstly, we can remove 45 by subtracting it from 180.
(45 - 45) + x(2) = (180 - 45)
x(2) = 135
From there, we can use inverse operations again and divide to remove the multiplication.
x (2/2) = (135/2)
x (1) = (67.5)
x multiplied by 1 will still equal x, so we can simplify our answer to:
x = 67.5
Therefore, x is equal to 67.5.
Hopefully this helps! :)