a) $x+2 \times\sqrt{16}=-3\times\sqrt{49}$
$x + 2 \times 4 = -3 \times 7$
$x + 8 = -21$
$x = -29$
b) $2x-\sqrt{1.69}=\sqrt{1.21}$
2x - 1.3 = 1.1
x = 1.2
c)$ 5\times(\sqrt{\frac{1}{25}}-x)-\sqrt{\frac{1}{81}}=-\frac{1}{9}$
$ 5\times(\frac{1}{5}-x)-\frac{1}{9}=-\frac{1}{9}$
$ 5\times(\frac{1}{5}-x) = 0$
$\frac{1}{5}-x=0$
$ x= \frac{1}{5}$
d)$2+\frac{1}{6}-x = 10\times\sqrt{0.01}-\sqrt{\frac{25}{36}}$
$2+\frac{1}{6}-x = 10\times0.1-\frac{5}{6}$
$2+\frac{1}{6}-x = 1 -\frac{5}{6}$
x = 2