On page 90 of the first volume of Grade One Mathematics, the second question is to find a rule to fill in the number 5+5+5 = (5). The title of page 90 of the first volume of senior one mathematics is regular number filling, and the answer is 4+4+4 = (4). 5+5+5=(5)。 (6)+(6)+(6)=( 18)。 12-4-4-4=0。 15-5-5-5=0。 18-(6)-(6)-(6)=(0)。 2+5+3= 10。 5+ 1+9= 15。 8+3+7= 18, 10+40+30=(80)。 20+ 10+(30)=60。 (40)+30+20=90。