We are to show that if X ⊆ Y then (X ∪ Z) ⊆ (Y ∪ Z) for sets X, Y, Z.
Assume that a is a representative element of X, that is, a ∈ X. By the definition of union, a ∈ X ∪ Z. Now because X ⊆ Y and we assumed a ∈ X, then a ∈ Y by the definition of subset. And because a ∈ Y, then a ∈ Y ∪ Z by definition of union.
We chose our representative element, a, and showed that a ∈ X ∪ Y implies that a ∈ Y ∪ Z and this completes the proof.
The angle whose sine is 0.39581 is 23.31650126° (round it how you want).
To calculate this, you need to do the inverse sine of 0.39581.
Inverse sine looks like

, however, it is not the sine of the angle to the power of -1.
Answer:
31.25 or 31 1/4 cups
Step-by-step explanation:
1 1/4 = 36
x = 900
=> 5/4 = 36
x = 900
Cross multiply
=> 5/4 * 900 = 36 * x
=> 4500/4 = 36x
=> 1125 = 36x
=> 1125 / 36 = 36x / 36
=> 31.25 = x
31.25 = 31 1/4
So, 31.25 or 31 1/4 cups are required for 900 cupcakes.
The total monthly bill of the gym = $53
The cost of membership of a month = $25
Let 'n' be extra the number of hours Bella worked on.
The cost for working on extra hours = $4
So, we have to determine the equation, Bella worked out after hours.
We will determine the equation by:
(Monthly cost of membership) + ( cost for extra hours
number of hours extra worked on ) = Total monthly bill received
So, we get

$25+4n = $53 is the required equation.
Therefore, $25+4n = $53 equation can be used to determine how many times Bella worked out after hours.