4. a) (0,8·7+0,64)·(1,25-4/5-1,25)+31,64

1. Calculate the first parenthesis: (0.8 * 7 + 0.64) = (5.6 + 0.64) = 6.24.
2. Calculate the second parenthesis: (1.25 - 4/5 - 1.25) = (1.25 - 0.8 - 1.25) = -0.8.
3. Multiply the results and add 31.64: (6.24 * -0.8) + 31.64 = -4.992 + 31.64 = 26.648.