Answer:
a = 

Explanation:
Given
2b - 
 = - 

Multiply through by 2cd to clear the fractions
4bcd - 2ad = - c ( subtract 4bcd from both sides )
- 2ad = - c - 4bcd ( multiply through by - 1 to clear the leading negative )
2ad = c + 4bcd ( divide both sides by 2d )
a = 
