combine like terms
ax+bx=(a+b)x
just like distributive property
3x+4x=(3+4)x=7x
just add the coefieicnets
allso, remember you can do ANYTHING to an equation as long as you do it to BOTH SIDES
7a-3a+2a-a=16
7a-3a+2a-1a=16
7-3=4
2-1=1
now we have
4a+1a=16
4+1=5
now we have
5a=16
divide both sides by 5
5a/5=16/5
5/5a=3 and 1/5
1a=3 and 1/5
a=3 and 1/5
a=3 and 1/5 or 16/5