Will someone find the value of x for these two questions?

Which expression do you get when you eliminate the negative exponents of 4a^2 b^216a^-3 b

Afurniture store is having a weekend sale and is offering a 20% discount on patio chairs and tables the sales tax on furniture is 6.25%

One cell phone plan charges $20 per month plus $0.15 per minute used. a second cell phone plan charges $35 per month plus $0.10 per minute used. write and solve an equation to find the number of minutes you must talk to have the same cost for both calling plans.