Answer:
He answered 7 true/false questions correctly
Step-by-step explanation:
True / False : 2 points each
Multiple choice: 4 points each
Assuming he answered "x" true/false questions and "y" multiple choice questions. You can write the information in the form of equations:
Points in test = 2*(true/false) + 4*(multiple choice)
86 = 2*x + 4*y
18 = y
Replacing y = 18 in the first equation:
86 = 2*x + 4*18
86 = 2*x + 72
14 = 2x
x = 7