(d) Let the principal be ₹ P and rate of interest be r.

Given, t = 2 yr

Amount = P

(1+)t = P

(1+)2Cl = Amount - Principal

= P

(1+)2 - P

According to the question,

P

(1+)2 - P = 5520

........(i)Again, principal = ₹ P, rate = r and time = 3 yr

SI =

=

According to the question,

= 7200 ⇒

=⇒ r =

∴ r =

.........(ii)On putting the value of r in Eq. (i). we have

P

(1+)2 - P = 5520

⇒ P

(1+)2 - P = 5520

⇒ P

[1+()2+] - P = 5520

⇒ P +

+ 4800 - P = 5520

⇒

= 55520 - 4800

⇒

= P

∴ P = 8000

On putting the value of P in Eq (ii), we get

r =

= 30

Therefore, rate of interest is 30% per annum.