Can i pls have help with is so confused

500.

Solution:  210 is 42% of X  

Equation: Y = P% * X  

Solving our equation for X

X = Y/P%

X = 210/42%  

Converting percent to decimal:

p = 42%/100 = 0.42  

X = 210/0.42  

X = 500

i know the answer is 3

step-by-step explanation:

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.