[R] optima setting of multiple response

[EMA_CHO at promos.com.tw]

Dears:
I have a question about multiple response and find the optima setting.
There are 7 responses(y1,y2,y3,y4,y5,y7,y8) and 5 variables(x1-x5).

y1=0.3567+ 0.0154*x1-0.0003*x2+ 0.2295*x3-0.0082*x4
y2=278.6814-4.3832*x1+0.0831*x2-24.3953*x3+8.1404*x4
y3=8.9813-0.0025*x2-0.1746*x3+ 0.0560*x4+ 0.0346*x5
y4=220.216+1.204*x2+53.634*x4-15.473*x5
y5=1.1404+0.0644*x3-0.0278*x4-0.0044*x5

y7=8.9155-0.0042*x2-0.1647*x3-0.2026*x4+0.0538*x5
y8= -22.5899+0.0719*x2+4.2494*x4


subject to
0.783< y1 <0.957
324< y2 <396
8.1< y3 < 9.9
0.9< y4 <1.1
0.585< y5 <0.715
8.1< y7 < 9.9
0.9< y8 <1.1
3< x1 < 6
260< x2 < 460
2< x3 < 4
1< x4 < 10
35< x5 < 45


Which function or package can I us?
I have try the "lp" function but there is no solution.

Thanks for your answer.