$$50\cdot a=30\cdot100$$  

$$30\cdot a=100\cdot50$$  

$$100\cdot a\ =\ 30\cdot50$$  

$$\frac{b}{24.50}=\frac{35}{100}\$$  

then do 24.50 + 5.08

$$\frac{b}{24.50}=\frac{35}{100}\$$  

Then do 24.50 - 5.08

$$\frac{b}{24.50}=\frac{35}{100}\$$  

then b = 5.08

$$\frac{b}{24.50}=\frac{35}{100}\$$  

then do 24.50 + 5.08

$$\frac{b}{24.50}=\frac{35}{100}\$$  

Then do 24.50 - 5.08

$$\frac{b}{24.50}=\frac{35}{100}\$$  

then b = 5.08