Answer :

To find the value of [tex]\( r \)[/tex] when [tex]\( r \% \)[/tex] of 70 is 21, follow these steps:

1. Understand the relationship: [tex]\( r \% \)[/tex] of 70 implies that [tex]\( r \)[/tex] percent of 70 is equal to 21. Mathematically, this can be written as:
[tex]\[ \frac{r}{100} \times 70 = 21 \][/tex]

2. Convert the percentage to a decimal: Recall that [tex]\( r \% \)[/tex] is the same as [tex]\(\frac{r}{100} \)[/tex].

3. Write the equation: Substitute the known values into the equation:
[tex]\[ \frac{r}{100} \times 70 = 21 \][/tex]

4. Solve for [tex]\( r \)[/tex]:
[tex]\[ \frac{r \times 70}{100} = 21 \][/tex]

5. Isolate [tex]\( r \)[/tex] by multiplying both sides of the equation by 100 to eliminate the denominator:
[tex]\[ r \times 70 = 21 \times 100 \][/tex]
[tex]\[ r \times 70 = 2100 \][/tex]

6. Finally, divide both sides by 70 to solve for [tex]\( r \)[/tex]:
[tex]\[ r = \frac{2100}{70} \][/tex]
[tex]\[ r = 30 \][/tex]

Thus, the value of [tex]\( r \)[/tex] is [tex]\( 30 \)[/tex].