420.

9+13:2

22:2=11

421

 x+y:2 = 15
x + y = 15.2
x + y = 30

422

x-y=7
x=7+y
7=7+y:2=12
14+y=24
y=10
x=17

349.

BC^2=BH^2+AC^2

BC^2=6^2 +4^2

BC^2=36+16

BC^2=52

VC^2=V52=2V13

350.

351.

S=1/2*ADBC=1/2*24*30=360

352.

353.

P=32

AB+BC+AC=32

5x+5x+6x=32

16x=32

x=2

S=VP/2(P/2-AC)(P/2-BC)=V6*2*2*4=4*6*2=48