F(t)=−2t+5f, left parenthesis, t, right parenthesis, equals, minus, 2, t, plus, 5 f\Big(f(f, left parenthesis
\Big)=13)=13

1; 35 is the ratio

step-by-step explanation:

this is a direct variation proportion. y = kx

y is the total amount due, k is the constant of variation, and x is the number of texts sent.

plug in the 3.20 and the 16 to solve for the "k". this is the constant of proportionality. it is the value that will not change.

3.20 = k(16). solving you get $.20 per text.

the equation would then be y = .20x

i don't even know how to read that, ill try to do it if you translate it into english.