I am running two separate t-tests and have created one table for the results which I want to export to LaTeX. I require the total number of observations for each subgroup (so four in total) at the bottom of the table. None of the subgroups have missing data. Any help would be much appreciated. Thanks.

Code:
sysuse auto, clear

local vars "turn mpg weight"

gen price_d = (price>5000)

est clear
eststo ttest_1: estpost ttest `vars' if price_d==1, by(foreign)
eststo ttest_2: estpost ttest `vars' if price_d==0, by(foreign)

esttab ttest_1 ttest_2 using "auto.tex", replace booktabs label alignment(S S) ///
    cells("mu_1(fmt(3)) mu_2(fmt(3)star)") collabels("Expensive" "Cheap") ///
    mgroups("Domestic" "Foreign", pattern(1 1) prefix(\multicolumn{@span}{c}{) suffix(}) span erepeat(\cmidrule(lr){@span})) ///
    star(* 0.10 ** 0.05 *** 0.01) ///    
    noobs nomtitles nonum prehead({\begin{tabular}{l*{2}{cc}}\toprule)