if you use the desmos graphing calculator - since you didn't provide answer choices - it should be able to help you.
To make a square for x²+bx=c, add(

)²on both side
in this case, b is-3/4, half of b is -3/8, and (-3/8)² is 9/64, so you add 9/64 to both side.
9/10 or 0.9
Hope this helps
Answer:
C=5
Step-by-step explanation:
3^ + 4^2 = 25
and the square root of 25 is 5 therefore C=5