143.3-15.25 cosh(0.0438x)=0
Subtract 143.3 from both sides
-15.25cosh(0.0438x) = - 143.3
Divide both sides by -15.25
cosh(0.0438x) = 143.3/15.25
Take the arccosh to isolate x
arccosh(143.3/15.25) = 0.0438x
Divide both sides by 0.0438
arccosh(143.3/15.25)/0.0438 = x = about 66.9102
As I'm not overly familiar with these functions, WolframAlpha also gives the negative of this as the other [real solution] x intercept......here's a pic :

