Number of orders Lisa served: | |

Number of orders Tom served: | T=L-5, so L=T+5 and T -L= -5 |

Number of orders Hans served: | H=2L, so L=H/2 and H - 2L = 0 |

T+H+L=71 |

T+H+L=71

Putting everything in terms of one variable.

(L-5)+2L+L=71

Solve for L

then solve for T=L-5 using what you found for L

then solve for H=2L using what you found for L.

You could also

T - L = -5

H -2L= 0

H + T+ L =71

And solve the 3 variable simultaneous equations.