1. The problem statement, all variables and given/known data

hi

i am wondering if this is correct. this is the question;

Three cells, each of e.m.f. 1·5 V and internal resistance 0·50 Ω, are connected in series to

make a battery of e.m.f. 4·5V. The battery is connected to a resistor, R, of resistance 6·0 Ω.

2. Relevant equations

V= i/R

3. The attempt at a solution

TOTAL VOLTAGE = 4.5V

TOTAL RESISTANCE = 6.5 OHMS

but the answer states the total resistnace is 7.5 ohms.

can someone kindly explain how?

thanks