R help - Feb 2004 - Fit system of equations

Hi R-masters

I have this system of equations

R(x,t)= a(t)+b(x,t)
a(t) = c + d*t
b(t) = e + f*t

where 
x is a vetor of age<-c(37,42,47,52,57,62,67,72,77,83),
t is vetor of year (1980:2000)
R(x,t) = Rate of mortality in age x on year t
a(t) = base mortality on year t
b(x,t) = exponential rate of mortality for age x on year t
b(t) = exponential rate of mortality on year t

I wish is possible fit this system in R?
Case positive Which the best method?



Thanks in advance

Bernardo Rangel Tura, MD, MSc
National Institute of Cardiology Laranjeiras
Rio de Janeiro Brazil