f <- c(10,3,7,4)
A <- rbind(
  c(1,1,1,1),c(1,0,0,0),c(0,0,0,1),c(-0.5,1,0,0)
)
l <- c("<=","<=","<=",">=")
b <- c(500000,200000,100000,0)
r <- lp("max",f,A,l,b)
r$objval
r$solution