How to solve algebraic expression using pemas( excuse my aunt sally)

Its actually PEMDAS you forgot the D. 
P-parentheses ()   E-exponents     M-multiplication  D-division    A-addition   S-subtraction.  

Example: 3(2+4)-6

You would add 2 and 4 first, since they are in parentheses. Then you'd have:

3(6)-6

Then you would multiply 3 and 6, since multiplication comes before subtraction in PEMDAS. so then you'd end up with:

18-6

Which, 18-6=12.

Hope this is what you were asking for, and I hope this helps!! :)