Answer:
20
Explanation:
You can write the equation x+(3x+1)+(x-11)=90 and then isolate x
x+(3x+1)+(x-11)=90
5x-10=90 (combine like terms)
5x-10+10=90+10 (add 10, addition property of equality)
5x=100
5x/5=100/5 (divide by five, division property of equality)
x=20