A soil sample near Chernobyl was found to contain 187 kBq/m² of cesium-137. If the half-life of cesium-137 is approximately 30 years, how much cesium-137 will remain in the sample after 90 years? 93.50 kBq/m²
23.38 kBq/m²
6.23 kBq/m²
1.58 kBq/m²

Ithink the answer is c

Forensic inspection of the rom or persistent memory does not include overwritten or erased text files e-mails sent web sites visited recently password-protected records

Yep i just took this test

You need to figure out at which x-value does the graph has a tangent line slope of -1.remember, the derivative is the slope of the tangent line. so find the derivative function and set it to equal -1 to find the x-value that will have a tangent line slope of 0.differentiate with the chain rule.    set the derivative to equal -1 and solve for x.      take log base 10 of both sides. also recall that  .    so the x-coord of the point of tangency is .the y-coordinate of this point of tangency can be calculated using the original function:     using point-slope form, the equation of the tangent line is      the x-intercept of this tangent line is when the graph is at y=0.    this rounds off to  .choice c.