3(5^x) is an exponential function.and which rise very fast y = 127 - 2x is a line Which decrease wçith a 2 slope f(0) = 127 3.5^2 = 75 and 3.5^3 = 375 I guess the intersection will be between 2and 3 lets put both the functions in a graph calculator window: x between 2 and 3 y between 75 and 127 I have an intersection between 2 and 3 use the "table" of the calculator we can see that the intersection is between 2.3 and 2.4 try again range: start:2.3 end 2.4 intersection is in [2.3;2.31] lets say it's 2.305