1.149 Нужно решение.

Элементарная система:

$\left \{ {{a-b=\frac{7}{18}} \atop {a+b=\frac{5}{27}}} \right.$

$\left \{ {{a=b+\frac{7}{18}} \atop {b+\frac{7}{18}+b=\frac{5}{27}}} \right.$

$\left \{ {{a=b+\frac{7}{18}} \atop {2b=\frac{30-63}{162} }} \right.$

$\left \{ {{a=-\frac{33}{81}+\frac{7}{18}} \atop {b=-\frac{33}{81} }} \right.$

$\left \{ {{a=-\frac{66-63}{162} \atop {b=-\frac{11}{27} }} \right.$

$\left \{ {{a=-\frac{1}{54} \atop {b=-\frac{11}{27} }} \right.$