45% of 160 + ? % of 180 = 19 % of 900

$frac{{45}}{{100}} imes 160 + frac{?}{{100}} imes 180 = frac{{19}}{{100}} imes 900$

$72 + frac{?}{{100}} imes 180 = 171$

$frac{?}{{100}} imes 180 = 171 - 72$

$frac{?}{{100}} imes 180 = 99$

$? = frac{{99 imes 100}}{{180}} Rightarrow ? = 55$