insert childs into I: 115=3*(33-adults)+5*adults 115=99-3*adults+5*adults 16=2*adults 8=adults
insert adults into II: 33-8=childs 25=childs
so it's the last option
question 7) a) y<6 and y>2 can also be written as 2<y<6, so solution 3 exist for example b) y>6 and y>2 can also be written as 2<6<y, so solution 7 exist for example c) y<6 and y<2 inverse of b: y<2<6, so for example 1 d) y>6 and y<2: y<2<6<y, this is impossible as y can be only either bigger or smaller than 2 or 6
so it's the last option
question 8) I: x+y=12 II: x-y=6
subtract: I-II: x+y-(x-y)=12-6 2y=6 y=3
insert y into I: x+3=12 x=9
(9,3)
question 9) I: x+y=6 II: x=y+5
if you take the x=y+5 definition of II and substitute it into I: (y+5)+y=6
