Приводим к общему знаменателю:
(36*(20+х)+22*(20-х)-3*(20+х)(20-х))/(20-x)(20+x) = 0
(720+36х+440-22х+3х²-1200)/(20-x)(20+x)=0
ОДЗ:
20-x≠0;x≠20
20+x≠0; x≠-20
3х²+14х-40=0
D = 196 + 480 = 676
x1 = (-14+26)/6 = 2
x2 = (-14-26)/6 = -40/6 = -20/3
Ответ:-20/3 ; 2