Because ratios can be written as fractions
[tex]\frac{mulch}{2.25}=\frac{gravel}{1.33}[/tex]
172 =[tex]\frac{mulch}{2.25}+ \frac{gravel}{1.33}[/tex]
172 - [tex]\frac{mulch}{2.25}[/tex] = [tex]\frac{gravel}{1.33}[/tex]
76.44 mulch = x amount of gravel = 172
Gravel = 172 - 76.44
= 95.56