How do i calculate these percentage weights?

First test: 63/80 - Weight = 30%



Second test: 14/30 - Weight = 20%



Third test: Weight = 50% - What will i need in order to get a pass in this Third test (out of 100% weighting)How do i calculate these percentage weights?
imagine the weighing is points i.e 30% = 30 points



63/80 x 30 = 23.63

14/30 x 20 = 9.33



sum = ~33

assuming passing overall is 50% then you need another 17 points



if 3rd test is out of 100, then you need 17