a) X x 15 - X : 0,1 = 2
X x 15 - X : $\frac{1}{10}$ = 2
X x 15 - X x 10 = 2
X x (15 - 10) = 2
X x 5 = 2
X = 2 : 5
X = 0,4
b)X + X : 2 = 0,36
X + X x $\frac{1}{2}$ = 0,36
X x (1 + $\frac{1}{2}$ ) = $\frac{9}{25}$
X x $\frac{3}{2}$ = $\frac{9}{25}$
X = $\frac{9}{25}$ : $\frac{3}{2}$
X = $\frac{9}{25}$ x $\frac{2}{3}$
X = $\frac{6}{25}$