Question

Next week your math teacher is giving a chapter test. The test will consist of 35 questions. some problems r worth 2 point and some r worth 4 points. there are 20 questions worth 2 points. how many problems are worth 4 points. solve by substitution

Answer 1

There are 15 questions worth 4 points 

Answer 2

There are 35 total questions. You already know that 20 of the questions are worth 2 points. You subtract 20 from 35. 35-20=15. So 15 questions are worth 4 points.
Total questions~35. Worth 2 points~20. Worth 4 points~15.