10+2(x)=5(x-7)
10+2(x)=5(x)-35
35+10=5(x)-2(x)
45=3(x)
45/3=x
x=15
Answer:

Step-by-step explanation:
We are required to solve for c in the equation: 
Step 1: Collect like terms

Step 2: Find the Lowest Common Multiple of the denominators
LCM of 8 and 5 is 40
Step 3: Multiply all through by 40

Step 4: Simplify
40c=32-5
40c=27
Step 5: Divide both sides by 40 and simplify if possible.

Answer:
y = -⅔x + ²²/₃
Step-by-step explanation:
1. Calculate the slope of EF
Assume E is at (-2, 5) and F is at (1, 3).
m₁ = (y₂ - y₁)/(x₂ - x₁) = (3 - 5)/(1 -(-2)) = -⅔
2. Calculate the slope of the parallel line
m₂ = m₁ = -⅔
3. Calculate its y-intercept
y = mx + b
6 =-⅔(2) + b
Simplify
6 = -⁴/₃ + b
Add ⁴/₃ to each side
b = 6 + ⁴/₃ = ¹⁸/₃ + ⁴/₃ = ²²/₃
The y-intercept is at (0,²²/₃).
4. Write the equation for the line
y = -⅔x + ²²/₃
The diagram shows EF in red. The parallel line in black passes through (2, 6) with a y-intercept at (0,²²/₃).
From cosine law
c^2 = a^2 + b^2 -2abcos(C)
cos(C) = (a^2 + b^2 - c^2)/2ab
this formula will solve your problem