(12*5/13+Y)-9*9/13=7*7/13

(12 * 5/13 + у) - 9 * 9/13 = 7 * 7/13;

(60/13 + у) - 81/13 = 49/13;

60/13 + у = 49/13 + 61/13;

60/13 + у = 110/13;

у = 110/13 - 60/13;

у = 50/13;

(12 * 5/13 + 50/13) - 9 * 9/13 = 7 * 7/13;

(60/13 + 50/13) - 81/13 = 49/13;

110/13 - 81/13 = 49/13;

49/13 = 49/13.