2(4/9a - 0.5b) - 0.7(1/7a - 0.5b)

First, distribute the 2 and the -0.7:

(8/9a - b) - (0.7/7a - 0.5b)

Next, simplify the fractions:

(8/9a - b) - (0.1a - 0.5b)

Now, distribute the negative sign in the second set of parentheses:

8/9a - b - 0.1a + 0.5b

Combine like terms:

(8/9 - 0.1)a + (0.5 - 1)b

Now, simplify the coefficients of a and b:

(0.888a - 0.5b)