Answer:
since 2x = z
replace z with 2x
900000 = x+y+z
900000 = x+y+2x
900000 = 3x+y - eqn (1)
79750= 0.08x +0.09y+0.01z
79750 = 0.08x +0.09y+0.01(2x)
79750 = 0.08x+0.09y+0.02x
79750 = 0.10x +0.09y - eqn(2)
from eqn(1)
900000 = 3x + y
y = 900000-3x - eqn(3)
substitute eqn(3) in eqn(2)
79750 = 0.1x +0.09y
79750=0.1x + 0.09(900000-3x)
79750=0.1x+ 81000 - 0.27x
collect like terms
79750 -81000 = 0.1x-0.27x
-1250 = -0.17x
to find x divide both sides by -0.17
x = -1250/-0.17 ~= 7353
since 2x = z
2*7353 = 14706
in eqn(3)
y = 900000-3x
y= 900000-3(7353)
y = 900000-22059
y = 877941
x =7353,y= 877941,z=14706