The correct answer is 49:1.
This can be determined using the following simplified formula:
Maximum intensity/ Minimum intensity ( Imax/Imin) =[ ( a1+a2)/ (a1-a2) ]^2, where a1 is the first amplitude and a2 is the second amplitude
Now putting the values of a1 and a2 in the formula:
Imax/ Imin=[ (4+3)/(4-3) ]^2= 49:1
river lift system is where water from rivers is drawn directly to supplement irrigation schemes. river lift systems do not depend on the natural flow of water from rivers by gravity through canals, rather it employs other means such as pumps and direct .