4/45 - 1/30 = (4*2)/90 - (1*3)/90= 8/90-3/90= 5/90= 1/18
17/18 -11/12= (17*2)/36 -(11*3)/36 = 34/36 - 33/36 =1/36
Ответ: С
3*5=15
5*7=35
5*9=45
5*11=55
5*13=65
5*17=85
5*19=95
5*21=105
5*23=115
последняя цифра - 5
5+6*6*4=13*34=312
(5+8)*6=78+4=82
(5+8)*6=78-4=74
H= 1/2 * 24 * 20 = 20см
S= 1/2ah
S= 1/2 * 24 * 20 = 240 см кв.