I'm not sure how to do this manually but if you plug in 7/12 in a scientific calculator and then press sin -1 you'll get approximately 35.685
Answer:

Step-by-step explanation:
Let
denotes number of pencils, markers, erasers respectively.
For Andrea:

For Justin:

For Virginia:

On subtracting equations (i) and (ii), we get

Put
in equation (i)

Put
in equation (iii)

Multiply equation (iv) by 5 and equation (v) by 6 and then subtract both the equations.

Put
in equation 

Put
in equation (i)

Answer:
x = -4
Step-by-step explanation:
Multiply both sides by 2. Move constant to the right-hand side and change the sign. Add the numbers. And change the signs on both sides of the equation.
Answer: x=32
Step-by-step explanation:
Because a triangle is 180°, the missing angle in the triangle would be 60°.
Because of the 30°-60°-90° angles theorem, The side opposite 90° is double the side opposite 30°, which means that x=32.
Answer:
2x² + 6x + 20
Step-by-step explanation:
See the picture