Ratios are basically fractions and whatever they say first is the numerator (length in this case) and the second one is the denominator (width in this case)
Now just put them over each other and then get [tex] \frac{ \frac{15}{2} }{ \frac{11}{4} } [/tex]
Now just multiply each one by 4/11 to make the denominator 1 and get 60/22
Simplify and get 30/11
Thats your answer, 30/11 OR 30:11