How do we say that the cost of rice and the quantity of rice we purchase are in inverse proportion?​

This is different from the first one can someone me

The length of a rectangle is x times the square root of 100. the width is one-half y more than three-halves x. given that the area of the rectangle is 125 cm2, which equation could represent the rectangle in terms of x and y? a) 5xy − 15x = 125 b) 5xy + 15x = 125 c) 15x2 − 5xy = 125 d) 15x2 + 5xy = 125

In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class