Answer:
85°
Explanation:
We need to use the angle fact that angles in a quadrilateral add up to 360° and that a right angle is 90°, using this information we can for an equation to find the value of 1. Lets call "1" x so we don't confuse it with an angle. So,
x + 85 + 100 + 90 = 360
In an equation our aim is to find the value of what we are looking for as well as keeping the equation balanced. For example if we took away 90 only from one side then the equation would change so it's an important rule to keep in mind when solving equations, that you need to keep both sides of the equation the same.
x + 85 + 100 + 90 = 360
→ Simplify equation
x + 275 = 360
→ Minus 275 from both sides to isolate x
x = 85
The measure of angle '1' is 85°