Final answer:
After substituting x with 9 in the equation 5x + 6y = 90 and solving for y, the correct value of y is determined to be 7.5, making option (a) correct.
Step-by-step explanation:
To find the value of y that makes the equation 5x + 6y = 90 true when x = 9, you can substitute the value of x into the equation and solve for y.
Substitute x = 9 into the equation:
5(9) + 6y = 90
45 + 6y = 90
Now, subtract 45 from both sides:
6y = 45
Divide both sides by 6 to solve for y:
y = 46/6
Simplify the fraction:
y = 7.5
Therefore, the correct answer is: a) 7.5
The value of y that makes the equation true when x = 9 is 7.5.