As we know,

The formula for S.I = P*R*T/100.

And Amount = P + S.I.

Now,

Let the sum of money be 100 rupees.

In 9 years it becomes 7 times. Therefore,

100×7=700 in 9 years.

Now According to simple interest formula.

A=P(1+rt)

Where A= final amount

P= Principle amount

r= rate.

t= time

Now on putting the values and solving it we get

700=100(1+ 9r)

From this equation we get r= 0.66 or 66.66%

Now putting the values in the equation again to solve for the number of years required to get the initial amount multiplied 49 times.

4900=100(1+66.66t)

Ans t= 0.72 or 72 years