You have to distribute the number outside the parenthesis to the numbers in the parenthesis, so basically 0.5 x 2a and 0.5 x -3 and for the other side 0.4 x 6 and 0.4 x 2a.
You will get:
a - 1.5 - 0.1 = 2.4 + 0.8a
Simplify:
a - 1.6 (because negative minus a number decreases the number)
Equation:
a - 1.6 = 2.4 + 0.8a
Subtract 0.8a from both sides.
0.2a - 1.6 = 2.4
Add 1.6 to both sides.
0.2a = 4
Divide by 0.2 (or as a fraction 1/5)
4/0.2 or 4/1/5 which is 4 x 5 because dividing a fraction is multiplying the reciprocal.
a = 20
