[tex] - 5.2a \times ( - 4.25b) = \frac{52 \times 17}{10 \times 4} ab = \\ \frac{221}{10} ab = 22.1ab [/tex]

[tex]9y + 8x - 25 y - x = \\ (9 - 25)y + (8 - 1)x = \\ 7x - 16y[/tex]

[tex]a - (18 + a) + ( - a - 30) = \\ a - 18 - a - a - 30 = \\ - a - 48[/tex]