PLEASE answer 'I'll mark you brainliest "if" it's correct'

Answer:
3x+4
Step-by-step explanation:
3 ft every second is the rate of change or the slope. 4 ft above the ground is the y-intercept.
Answer:
y=3x+4
Step-by-step explanation:
3x is 3 feet multiplied by however many seconds
4 is the additional 4 feet that the balloon had started at