[tex] \frac{31,50}{x}=\frac{42}{100}[/tex]
The right fraction represents the percentage; 42 over 100 (100 is the total), or 0.42.
The left fraction is the part number over the whole number. The whole number is unknown, so we use 'x'.
[tex] \frac{31.50}{x} = \frac{42}{100}\\\\cross\ multiply\\\\31.50\times100=3150\\42\times x=42x\\\\3150=42x\\x=75 [/tex]
Your answer is 75.
