<h2>Answer: a = ¹/₂ (4 + b)</h2><h3>Step-by-step explanation:</h3>
To solve for 'a' we have to make it the subject of the equation. Since there are two unknowns ('a' & 'b'), we won't get a numerical value of 'a', but an expression in terms of the second unknown 'b'.
Since 2a - b = 4 <em> [add 'b' to both sides]</em>
then 2a = 4 + b <em>[divide both sides by 2 = multiplying by ¹/₂]</em>
