$K_{sp}$ $=$ $[M^{+3}] [OH^-]^3 $=$ s(3s)^3$
$⇒$ $27s^4 $= $27 \times10^{-12}$
$s = 10^{-3} [OH^{-1}] = 3s = 3 \times 10^{-3}$
$(I){\mkern 1mu} C{H_3}CH_2^ - {\mkern 1mu} + {\mkern 1mu} \mathop {C{H_3}N{H_2}}\limits_{p{K_a} = 35} \rightleftharpoons \mathop {C{H_3}C{H_3}}\limits_{p{K_a} = 50} + C{H_3}N{H^ - }$
$(II){\mkern 1mu} {F^ - }{\mkern 1mu} + {\mkern 1mu} \mathop {{H_2}O}\limits_{p{K_a} = 15.7} \rightleftharpoons \mathop {HF}\limits_{p{K_a} = 3.2} + H{O^ - }$