A function notation is expressed as f(x) = ax^b + cx^d + ..... where f(x) is equal to y, In this case, to rewrite 3x + 4y = 10 using function notation, we rearrange the statement and express in terms of x only. Hence
4y = 10 - 3x
y = (10 - 3x) /4 = f(x)
f(x) = 2.5 - 0.75x