first, start off with the number of double basses. the question says there are 4. now, add up all of the numbers of instruments in order to find the total. 7+4+11+11+11=44 (three 11’s for the first violins, second violins and violas). now since you’re comparing the double basses to the total amount, the ratio is 4/44. You can also simplify this ratio by dividing both numbers by 4, which will become 1/11. Now, in order to find the decimal, just divide the fraction. 1/11=.09 repeating. Hope this helped!