Yeah not just one letter but two letters perpendicular to another two letters. Each 2 letters like AB is a straight line which is crossed by another 2 letters making it perpendicular.
-3 and 4......................
Answer: 
<u>Step-by-step explanation:</u>

Restriction: 6x + 3 ≠ 0 <em>denominator cannot be zero</em>
<u> -3 </u> <u> -3 </u>
6x ≠ -3
<u> ÷6 </u> <u>÷6 </u>
x ≠ 
It would have to be number 2 if it's a dotted line, all the other options are incorrect unless you made a mistake with one or two of the symbols.