Question 9290
the first step is to set up your equation

I am going to set x=bonds and y=cds

equation one        
x+y=20000           

equation 2
x=y+3000

substitute equation 2 back into equation 1

(y+3000)+y=20000
2y+3000=20000
2y=17000
y=8500(cds)

now you can take this y value and plug it back into either equation you want

x=8500+3000
x=11500(bonds)