Question

P=s1+s2+s3 solve for s3

Answer 1

P=s1+s2+s3

Move +s1 to the other side. Sign changes from +s1 to -s1

P-s1=s1-s1+s2+s3

p-s1=s2+s3

Move s2 to the other side. Sign changes from s2 to -s2

p-s1-s2=s2-s2+s3

p-s1-s2=s3

Answer: p-s1-s2=s3