Respuesta :
Formula for compound interest is
Interest = Amount - Principal
Interest = [tex] P(1+r)^{t} [/tex] - P
Where r = rate in percent
t = time in years
For Jaina,
P = $300
r= 7%
t = 3 yrs
So, Interest = [tex] 300(1+0.07)^{3} [/tex] - 300
For Tomas
P = $400
r= 4%
t = 3 yrs
So, Interest = [tex] 400(1+0.04)^{3} [/tex] - 400
So pair of equations for Jaina and Tomas are
Interest = [tex] 300(1+0.07)^{3} [/tex] - 300
Interest = [tex] 400(1+0.04)^{3} [/tex] - 400