[R] plot custom x axis ticks values

[e-letter]

Readers,

For this data set:

testvalues<-c(10,20,30,40)

How to amend the plot instruction:

plot(testvalues,ann=FALSE,type='l',yaxt='n',xaxt='n')

so that x axis ticks labels can be added to existing graph with
arbitrary value such as 0,100,200,300)?

Thanks in advance.

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r2151