Help!!!Econometric question, thanks!!!!?

Use F-test to test hypothesis H0:b1+b2=0 in model of y=constant+b1x1+b2x2+b3x3+e in program of Stata, this question I got it....but the following question: use t-test to test a model and generate a t statistics directly that also test the previous hypothesis..... I'm really stuck with this quesiton......Thanks for any help!!!!!!!!!!!!!