Free points and maybe a brainlist

If (a, b) is the solution to the system of equations shown above, and a and b are integers, then what is the value of a+b?

17 a tourist was planning a trip by car for travelling at some constant speed for 2.5 hours. however, he found that if he increases the speed by 20 km/h he can cover the same distance in 30 minutes less time than it was planned. what was the planned speed of the tourist, in km/h?

Scientists observed a rock stratum with fossil. if mollusks evolved before arthropod, where will their fossils be found.