Start with

Add 2x to both sides:

Subtract 21 from both sides:

Divide both sides by 5. Since it is positive, we don't have to change the inequality sign:

So, the answer is 
Percent means parts out of 100
70%=70/100=7/10
7/10 of x=28
'of' means multiply
7/10 x=28
multiply both sides by 10/7 to get rid of fraciton
x=40
the number is 40
Answer:
833/500 or 1 333/500
Step-by-step explanation:
Answer:
C.
Step-by-step explanation: