// problem 7.3
b=2.5
d=2.5
C=56
A=b*(7.5+d)*0.5
P=2.5+((b*b+d*d)^0.5)*2
m=A/P
i=1/1200
Q=A*C*((m*i)^0.5)
disp(Q*1000,"the diacharge through the channel in litres/sec")